Manufacture of Leather 



By 

ALLEN ROGERS, Ph. D. 

PRATT INSTITUTE, BROOKLYN, N. Y. 



MANUFACTURE OF LEATHER 
Parts 1-3 



393 

Published by 

INTERNATIONAL TEXTBOOK COMPANY 

SCRANTON, PA. 



i\bl\o^U 



T6ns 



Manufacture of Leather, Parts 1. 2, and 3: Copyright, 1922, 1909, 1902, by Inter- 
national Textbook Company. 



Copyright in Great Britain 



All rights reserved 



Printed in U. S. A. 



International Textbook Press 
Scranton, Pa. 




80050 



^ 






CONTENTS 



Note. — This book is made up of separate parts, or sections, as indicated by 

their titles, and the page numbers of each usually begin with 1. In this list of 

contents the titles of the parts are given in the order in which they appear in 
the book, and under each title is a full synopsis of the subjects treated. 



MANUFACTURE OF LEATHER, PART 1 

Pages 

Heavy, or Firm, Leathers 1-45 

Intoduction 1- 3 

Definitions and classification; Hide structure. 

Treatment of Hides 4-18 

Soaking; Cold-sweat system; Warm-sweat system; Lim- 
ing; Unhairing and fleshing; Leidgen unhairing 
machine; Deliming; Plumping the hides. 

Sole-Leather Manufacture 19-45 

Methods of tanning; Oak leather; Oiling and drying; 
Rolling; Treatment of the hides; Bleaching; Union 
leather; Quick sole-leather tannage. 



MANUFACTURE OF LEATHER, PART 2 

Heavy, or Finn, Leathers — (Continued) 1-42 

Sole-Leather Manufacture — (Continued) 1-3 

Oak-tanned belting leather; Harness leather. 

Vegetable Tanning Materials 4—21 

Classification of tannins; Wood and bark extracts ; Ott 
bark mill ; Williams' patent bark shredder ; Vat leach- 
ing. 

Analysis of Tanning Materials 22-35 

Analysis of bark, wood, etc. ; Teas percolator extractor ; 
Determination of non-tannins ; Analysis of tanning 
extracts ; Analysis of tan liquors. 

Analysis of Leather 36-42 

Determiation of moisture ; Determination of ash ; Deter- 
mination of oil ; Determination of nitrogen ; Determina- 
tion of water-soluble materials ; Determination of 
glucose. 



iv CONTENTS 



MANUFACTURE OF LEATHER, PART 3 

Pages 

Limp, or Light, Leathers 1-54 

Process of Manufacture 1 

Automobile and Upholstering- Leathers. 2-0 

Stoning jack; Splitting machines ; Daubing; Embossing. 

Bag, Case, and Strap Leather 10-17 

Stuffing materials; Hand and drum stuffing; Fat-liquor- 
ing; Whitening. 

Side Leathers 18^20 

Shoe, Glove, and Fancy Leather 21-27 

Working out skins; Shaving; Staking; Seasoning; Sur- 
facing. 

Vegetable-Tanned Calfskins 27-29 

Vegetable-Tanned Sheepskins 30-31. 

Hogskins ■^^ 

Tawing • 32-34 

Oil Tannage • 35-37 

Chrome Tanning 38-48 

Two-bath chrome-tanning process ; One-bath chrome- 
tanning process; Fat-liquoring; Box calf; Matt calf; 
Glazed kid ; Chrome patent leather. 

Dongola Leather 48-49 

Leather Dyeing > 50-52 

Measurement of Leather 52-54 



MANUFACTURE OF LEATHER 

Serial 416A (PART 1) Edition 3 



HEAVY, OR FIRM, LEATHERS 



INTRODUCTION 

1. Definition and Classification. — The term leather 
is applied to the product obtained by the treatment of hides or 
skins of animals with certain reagents that convert the animal 
tissues into a tough, opaque, pliable, and fibrous substance 
which is not subject to putrefaction. 

2. The pelts of animals come to the tanner in four con- 
ditions : green or market (fresh from the animal) ; green salted 
(when salt has been rubbed on the flesh and the skins placed 
in piles to cure) ; dry salted (same as green salted but after- 
wards allowed to dry) ; flint, or dry, hides (usually stretched 
and allowed to dry in the sun). According to their size, these 
pelts are divided into three general classes, namely, hides, kips, 
and skins. Hides comprise the coverings of larger animals 
such as the cow, horse, camel, and walrus. These are used 
for heavy leather manufacture such as shoe soles, machinery 
belting, harness, and other purposes where stiffness and 
strength are required. They are also often split for the pur- 
pose of producing shoe leather, bag, case, strap, automobile, 
and furniture leather. Kips are the undersized animals of the 
same species. Skins are obtained from small animals such 
as sheep, goats, and calves. Kips and skins are used in the 

COPYRIGHTED BY INTERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 



2 MANUFACTURE OF LEATHER, PART 1 

manufacture of light leather for shoe uppers, pocketbooks, 
bookbinding, gloves, and fancy articles. Both hides and skins 
are graded according to weight and imperfections, the latter 
being in the nature of cuts, brand marks, hair slips, and grubs. 
Diseased hides are some times found and are a source of great 
danger to the tanner. 

3. Hides are obtained from the various slaughter houses 
over the country and are known as domestic, or native. They 
are also obtained from other parts of the world and are usually 
known by the name of the country from which they originate. 



hide: structure 

4. Analysis of Skins. — At first glance, the pelts of 
various animals appear to have little in common. On closer 
examination, however, a very close similarity will be observed. 
In structure, all animal skin is made up of several readily 
defined layers. The skin is not merely a covering for the 
animal, but also serves as a container for nerves and secretive 
glands, and as a bed, or ground, for the hair, or fur. It is 
made up of two principal layers : the epidermis, or cuticle, and 
the corium, or tnie skin. These two layers are totally distinct 
in structure, origin, and functions. 

5. The epidermis is a thin covering of the true skin 
and is entirely removed before the tanning operations begin. 
In life, the upper, or external, part is being constantly worn 
away, falling off in the form of dry scales. The interior part 
of the epidermis is made up of numerous living nucleated 
cells ; as the surface of this layer is reached, these cells 
become flattened and finally dry up and form the exterior part 
of the epidermis and ultimately drop off as dead scales. 
These cells, which renew the horny external tissue of the epi- 
dermis, are in turn renewed by vessels situated in the corium, 
or true skin. The epidermis does not combine with tannin 
and is therefore removed, laying bare the true skin, which is 
known to the tanner as the grain. 



MANUFACTURE OF LEATHER, PART 1 3 

6. The corium, or true skin, is the skin with which the 
tanning agents combine to form leather. There is an inter- 
mediate albuminous layer between the corium and the epidermis. 
Both layers are composed of interlaced bundles of fiber running 
across and above one another and parallel to the surface of 
the skin. These fibers are surrounded by fluid matter, which 
serves to keep the skin in a moist and pliable condition. On 
removal of this fluid the fibers alone remain, and if dried by 
a gentle heat they assume a horny appearance and become in 
substance about one-third of the raw hide. 

The corium determines the quality of the leather that can be 
made from a hide. Its thickness, flexibility, and strength are 
reproduced in the leather. Between the fibers of the corium 
is an albuminous substance called coriin: in a dry state this 
holds and connects the fibers. 

The connective tissue of the corium gives form to the skin, 
the intercellular substance, coriin, lying between the fibers. 
When boiled with water, these connective tissue fibers form 
glue, losing their organized structure, and making a homo- 
geneous jelly. 

7. The intercellular substance is probably a decomposition 
product of the connective tissue. This coriin is soluble in 
lime water and other alkaline solutions ; frequent treatment of 
the skin with these reagents withdraws fresh quantities of 
soluble matter with every treatment. This fact should be 
noted in connection with the liming of skins to remove the hair. 

Dilute inorganic acids swell the connective tissue. The 
swelling of the skin by acids is made use of to facilitate tanning ; 
it not only makes the skin more sensitive for the reception 
of the tanning material, but also effects the disintegration of 
the fiber bundles into individual fibers, thereby increasing the 
surface. 

8. The under skin is made up of loose connective tissue, 
embedded in which are the sweat and fat glands, the blood 
vessels, and muscular fiber. Fig. 1 shows an enlarged micro- 
scopic transverse section of the skin in which the Malpighian 
net, or lower layer of the epidermis, is shown at d ; the corium, 



4 MANUFACTURE OF LEATHER, PART 1 

iat h ; the lobules of adipose tissue, at m ; the external orifices of 
the sweat glands, at a'', a hair folHcle, at 3/; a shaft of hair in 

the hair follicle, at ^ ; a 
hair papilla, at i. At / 
is illustrated the con- 
nective tissue of the 
under skin, showing 
the sweat glands a, 
with the ducts c, 
through which the 
sweat passes to the sur- 
face of the skin; at k 
is shown a hair bulb, 
and at e are shown 
openings of the seba- 
ceous glands. The 
horny outside layer of 
the epidermis h shows 
hair, as at f, or wool 
at different places. The 
hair is not embedded 
immediately in the surface, but in the capsules, or sacs, being 
continuous with the epidermis and reaching down to the 
corium. 




Fig. 1 



TREATMENT OF HIDES 

9. Some operations in the manufacture of leather are fol- 
lowed, with more or less variation, in all branches of the 
industry, and, to save repetition, these will be treated generally, 
variations being noted in descriptions of the tanning processes 
necessary for the production of specific kinds of leather. 
These variations are so numerous that it will be impossible to 
enumerate them all, but enough will be noted to indicate what 
latitude exists in the application of the general principles 
involved. 

10. Soaking-. — Whatever may be the class of hide in 
use at the tannery, the first operation is that of soaking. 



MANUFACTURE OF LEATHER, PART 1 5 

This is always done by means of water, with or without the 
addition of chemicals. The various kinds of hides require 
different treatment as to mechanical handling, character of 
the soak, and the duration of the soaking. Whether the hide 
is green or has been dried with preservatives (in this case 
these preserving agents must be washed out), the dirt, 
blood, and dung must be removed, and the hide brought back 
to a state similar to that in which it was when taken from the 
carcass. All the foreign matter goes into the soaks, and only 
a short time elapses before the water becomes filthy. 

Where hard water is used, it is customary to add some 
softening agent, as borax, soda ash, or caustic soda, since 
soft water is better adapted to soaking purposes. Much 
valuable hide substance is lost in many tanneries through the 
use of soaks that have become putrid. An old soak gives 
better results than a new one, but if the vat is allowed to 
become putrid, depletion of the hide takes place, and the loss 
from this cause more than offsets the time gained. Plenty 
of pure water with a little borax or soda, if needed, is a much 
more effectual cleanser and softener than a putrid liquor. 

11. The general form of receptacle for the soaking is a 
pit or vat sunk in the ground. Wheels or drums have been 
used, and in some places are still employed, but the ordinary 
vat is the most convenient receptacle for the purpose. The 
hides are either hung in the water on racks or thrown in and 
spread out. Dried hides are generally placed in piles in the 
pits and the water then run on them. 

While in the soaks the hides must be watched by skilled 
workmen so that they will not become putrid. Thin hides 
must be removed as soon as they become soft, without wait- 
ing for the thicker ones to soften. The thin parts of all 
hides must be carefully watched, in order that they will not 
become damaged while the heavier parts are softening. 

12. Hide Mills. — Where heavy hides are being made 
into sole leather it is customary to use liide mills, also known 
as kickers, or stocks. A hide mill is merely a heavy iron shoe 
on the end of a vertical beam keyed at the other end. A 



6 MANUFACTURE OF LEATHER, PART 1 

backward-and-forward motion is imparted to the beam by a 
heavy shaft and the shoe moves in a heavy receptacle con- 
taining the hides. The hides are kept constantly in motion 
in contact with running water, and a couple of hours of this 
treatment is more beneficial than a day's quiet soaking. The 
hides are first put in the soaks until they become softened, and 
the mills are then used to finish the operation. Similar, but 
lighter, mechanical contrivances are used for the same purpose 
where lighter pelts are treated. 

Many tanners run the partly softened stock in a drum. 
Here the tumbling action helps materially to hasten the soften- 
ing. For green-salted hides it has also been found advantageous 
to do away entirely with pit soaking, simply depending upon 
milling the stock in the drum in the presence of running, water. 

13. Depilation. — Having brought the stock to a soft 
and clean condition, the next step is to remove the hair and 
epidermis, the operation being known as depilation. This 
may be accomplished in several ways, the oldest of which is 
known as sweating. Sweating may be carried out either in a 
cold or warm pit or cellar and is termed cold sweat or warm 
sweat. In both cases the results secured are due to incipient 
putrefaction. 

14. Cold-Sweat System. — ^As used in the United 
States, the cold-sweat system is carried out as follows : The 
sweat pits are vaults built of stone, with the proper apertures 
for ventilation, in order to regulate the temperature. Tight 
doors are provided, and these may also be used for ventilating 
purposes. After the hides are thoroughly soaked and softened, 
they are hung over poles or suspended by the edges in the 
sweat pit. The doors are closed until the putrefaction begins, 
and when this takes place careful watching is necessary. The 
hides are carefully scrutinized, and those in which the putre- 
faction is far advanced must be removed at once. The 
presence of a hide in the sweat pit for even a few hours after 
it is ready to come out, may spoil it. 

The sweating process hastens the expansion of the hide, 
opens the pores, and brings the hide back to a state analo- 



MANUFACTURE OF LEATHER, PART 1 7 

gous to that at the time of slaughter ; It gives to the dry, wild 
hide a much-needed development. During the putrefaction 
process much ammonia is generated as a result of decom- 
position. Efforts are being made to isolate the specific germ 
causing the putrefaction that loosens the hair. If these efforts 
are crowned with success and an antiseptic is found that will 
be fatal to germs other than those which cause putrefaction, 
the sweating process will be greatly simplified. 

After sweating, the hides are thrown into water or a weak 
lime bath, which stops further putrefaction. 

15. Warm-Sweat System. — As practiced in Germany, 
the warm-sweat system consists in placing the folded hides 
in an air-tight buried box, which is then covered with spent 
tan. Steam is frequently used to accelerate the sweating 
process, but its use is attended with great risk; the heat 
spontaneously generated by the hides is preferable. This 
system requires even more care than the cold-sweat process, 
because putrefaction promoted by heat makes rapid progress 
and may cause great loss. 

*If fresh-slaughtered hides are to be depilated by the sweat- 
ing process, the flesh side must be thoroughly salted and the 
hides then folded ; they are piled one on another and covered 
with straw. They are taken down after 18 or 20 hours, the 
hides opened and refolded, and again piled and covered, after 
which only occasional turning is needed to make the hair begin 
to slip. In the United States, most of the fresh-salted hides 
are limed and not sweated. 

16. Liming. — The depilation of hides is most commonly 
accomplished by placing them in a solution of lime until the 
hair bulb is loosened, when the hair can be readily scraped 
off. The lime acts on the roots of the hair and the hair 
sheaths are dissolved, but the hair itself is but slightly altered. 
Lime also acts on the skin; the fibers swell and absorb water, 
so that the skins become plump and swollen, and at the same 
time the substance that glues the fibers together is dissolved 



*In the United States the warm-sweat system differs from cold sweat 
only in regard to the temperature of the sweat pit. 



8 MANUFACTURE OF LEATHER, PART 1 

and the skins become a mass of finer fibers. The Hme also 
saponifies the natural fat, or oil, of the skin. 

17. Lime vats are made of timber or of masonry and 
are sunk into the ground so that the tops of the vats are on a 
level with the floor. The contents of the vats are made up 
by slaking the desired amount of quicklime and thoroughly 
plunging the solution. Generally, two or more lime vats of 
different ages are used, the hides remaining in one vat for a 
time and then being moved by means of hand reels between 
the vats, to the next lime vat. 

The time required for liming depends on the kind and 
condition of skins, conditions of the atmosphere, and the 
temperature of the limes in use. 

The question of when to throw away the limes is also an 
open one. Some tanners use them until they are almost 
saturated with decomposing matter extracted from previous 
hides. A lime in this state becomes a depilator by means of 
putrefaction and not because of its caustic action, but this 
should not be considered as good practice. 

18. Lime in excess must be present in the vats, so that 
a saturated solution of the hydrate of calcium is always sur- 
rounding the hides. Lime in solution is rapidly consumed 
in the depilation of the hides and must be constantly renewed. 
Much of the residue of the lime vats, generally mistaken for 
unused lime, is in reality a mixture of calcium hydroxide and 
calcium carbonate formed during the liming process. It is, 
therefore, found practical to add fresh lime from time to time 
to the vats and by frequent plungings keep it in suspension. 

19. Hydrated Lime. — In place of the older method of 
using lump lime, many tanners now employ the product 
known as hydrated lime. This form of lime is produced by 
adding just sufficient water to bring about the union between 
the calcium oxide and water, according to the following 
reaction 

CaO+H,0 = Ca(OH) 



MANUFACTURE OF LEATHER, PART 1 9 

The advantage of this material, which comes to the tanner 
in the form of a powder packed in bags, is that it may be kept 
indefinitely without change, and is always uniform in 
composition and action. 

20. Sodium Sulpiliide. — Sodium sulphide, when dis- 
solved in water and used as a depilating agent, has the prop- 
erty of quickly destroying hair and epidermis. It has the 
advantage of rapid action and the production of a tight leather, 
but has at the same time the disadvantage of a tendency to 
cause a drawn condition of the grain. For certain classes of 
leather, its use is desirable, in which case a 20° Bk.* solution 
is prepared in a paddle at a temperature of 70° F. The stock 
is entered and the paddle run for about 2 hours, when the 
wheel is stopped and after that it is run for 5 minutes each 
hour during the remainder of the day. The stock is kept 
in the liquor overnight and turned from time to time during 
the morning. At about noon the plug is drawn and the spent 
liquor discharged. The paddle is filled with water and run 
for half an hour. One per cent, of sodium bicarbonate is now 
added and the wheel turned for the same length of time. 
Fresh water is then turned on and the stock washed in running 
water for 3 hours. 

Sodium sulphide is sometimes used with lime. It forms 
caustic soda and calcium sulphide when it comes in contact 
with the lime. The calcium sulphide acts as a solvent for the 
hair and renders easier the removal of the very fine hair. The 
use of sodium sulphide shortens the unhairing process and 
causes less loss of hide substance as compared with lime, but 
it has the disadvantage of causing brittle, harsh leather unless 
it is carefully used in comparatively small amounts. The 
usual custom is to add the sodium sulphide in the first stages 
of depilation, the amount employed being about 10 per cent, 
of the lime taken. 

21. Sodium Sulphide and Calcium. Cliloride. — It 

has been found that a combination of calcium chloride with 

*See Manufacture of Leather, Part 2. 



10 MANUFACTURE OF LEATHER, PART 1 

the sodium sulphide will obviate the danger from drawn grain 
and the process is carried out as follows : Into the paddle is 
placed a weighed amount of sodium sulphide sufficient to pro- 
duce a 20° Bk. solution. To this solution is added 1 pound of 
calcium chloride for every 4 pounds of sulphide taken. The 
same method of handling is pursued as for straight sulphide, 
except that 2 per cent, of sodium bisulphite is used for 
neutralization in place of sodium bicarbonate. 

22. Arsenic sulphide is sometimes used in connection with 
lime and has the advantage that it does not produce a strong 
caustic condition. The form of arsenic sulphide employed 
is that known as realgar, or red sulphide of arsenic, having 
the formula AS2S2. 

23. Unliairing: and Fleshing-. — ^After the liming or 
sweating operation is completed, the hides are ready to have 
the loosened hair scraped off and to have the fleshy and fatty 
matter on the flesh side removed. These operations are 
known, respectively, as unhairing and fleshing. 

The unhairing and fleshing of hides is done both by hand 
and by machine. The latter method is supefseding the hand 
method only slowly, because of the care needed in operating 
the machine. An unskilful or careless operator may spoil 
hundreds of dollars' worth of hides in a day's work, and the 
greatest care and judgment must be exercised on the part of 
the workman while running the machine. 

The operations of unhairing and fleshing take place in what 
is known as the beam house. After the hair has been loosened, 
the hides are brought into the beam house ; if the sweat pit 
has been used to loosen the hair,' the hides are placed in cold 
water, which cools them and interrupts the putrefaction that 
has set in. Limed stock is generally unhaired without previous 
washing, being brought directly from the limes to the beam 
house. 

24. The beams on which the hand process of unhairing 
takes place are convex in shape, one end resting on the ground 
while the other is about the height of the workman's waist. 



MANUFACTURE OF LEATHER, PART 1 11 

Over these sloping beams the hides are spread and by means 
of a concave knife, the curvature of which conforms to that 
of the beam, the hair is removed. The operation is fatiguing, 
and only men of long experience, skill, and considerable 
strength, are employed. 

The knife is pushed against the hair, the sides being worked 
from the hind shank toward the head and then toward the 
back. In removing the short, fine hair, hides are occasionally 
damaged by having the grain cut ; to prevent this, a guard that 
projects beyond the edge of the knife and serves to protect 
the hide, is sometimes used. After the hair is removed, the 
hides are placed in water overnight and are then usually ready 
for fleshing. 

25. The operation of fleshing by hand consists in removing 
the fleshy and fatty matter by means of a sharp knife. The 
work requires great skill. Both straight and curved knives 
are used in the operation. The hide is thrown across the 
beam, which has first been covered by a hide already fleshed. 
The flesh is removed by long strokes of the knife, held in a 
slanting position, the right hand being uppermost. A long, 
steady drive results in fewer accidents to the hide than a 
short, choppy stroke. After the flesh has been removed from 
the main body of the hide, the hide is trimmed with a sharp 
knife and the shreds and projecting filaments are removed. 
All the fleshings are saved and sold for glue making. 

After fleshing, the hides are hung on individual sticks in 
vats of fresh water. If the hides are to be used for upper 
leather, the soaking is dispensed with and the hides at once 
bated. 

The hand method of fleshing and unhairing is slow, and 
has been almost entirely superseded by machines, which, if 
placed in the hands of skilled operators, do the work for 
about one-third of the former cost. 

26. Machine Fleshing and Unhairing. — ^With 
machinery, the hides are fleshed either after soaking and before 
liming or after they come from the limes. If fleshed before 
liming, they are generally run through the machine again after 

393—2 



12 



MANUFACTURE OF LEATHER, PART 1 



coming from the limes, in order to remove both the flesh left 
on after the first fleshing and the flesh raised up by the liming 
process. 

The machines that do the beam-house work are heavy, 
rigid affairs. The removal of the hair and flesh is accom- 
plished by rapidly revolving rolls, having raised irregular 
spines on their surface. 




Fig. 2 



27. The Leidg-en unliairing- maclime, Fig. 2, is an 
approved machine for unhairing. It consists of a revolving 
cylinder d supported on a steel frame that moves up and down 
in the arc of a circle, at the will of the operator, over a flexible 
bolster a on which the hide to be dehaired is placed. 



MANUFACTURE OF LEATHER, PART 1 13 

The hide or side is thrown flat on the flexible bolster a, the 
holder h is brought down and automatically clamps the end 
of the hide or side. The lever c is then thrown so as to put the 
machine in operation. The cylinder d, revolving at the rate 
of 190 revolutions per minute, moves down and up over the 
hide spread on the flexible bolster a. By reversing the lever, 
the revolving cylinder may be made to travel up and down 
within the space, of 2 or 3 inches. After the hair is removed 
from one end of the hide, the holder is released, the position 
of the hide on the bolster reversed, the holder again brought 
down and the remainder of the hair removed. Jets of water 
from a perforated pipe running behind the holder constantly 
play on the hide while it is being dehaired. 

The cylinder J is of cast iron, 6 inches in diameter, on the 
surface of which steel blades are inserted. The cylinder always 
revolves in the same direction whether passing up or down 
over the hide. The bolster a is securely fixed at the upper 
end and suspended at an angle of 45° ; at the lower end, by a 
system of weights and levers, an equal tension is produced at 
all times over the entire surface. Being supported only at the 
ends, the bolster is perfectly flexible over its entire surface, 
and the thick and thin parts of the hide are thereby subjected 
to even pressure. This machine will perform the work of 
6 men and, with a skilful operator, there is little danger of 
damage to the stock. 

28. For removing the flesh from the hide, the fleshing 
machine, shown in Fig. 3, is largely used in the tanneries of 
the United States. It consists essentially of a spirally bladed 
fleshing roll a^ past which the hide is fed by a rubber-covered 
bed roll h working in connection with a pair of fluted steel 
grip rolls c and d. 

The illustration shows the fleshing machine with grip rolls 
open, ready to receive the hide or side to be fleshed. The 
operator inserts the hide flesh side up between the parted 
rolls. A slight pressure on the treadle e causes the grip roll c 
to move down through the circular guides and take its place 
between the grip roll d and the rubber roll h. All three rolls 



14 



MANUFACTURE OF LEATHER, PART 1 



move forward, thus firmly gripping the hide and holding it in 
the proper position without damaging it. The revolution of the 
bed roll b and grip rolls c and d pulls the hide between 
the bed roll and the rapidly revolving fleshing cylinder a, which 
removes the flesh from the hide as it slowly passes under 
the cylinder. When the fleshing is completed, the treadle e is 
depressed, and while the rubber and front grip rolls are moving 




Fig, 3 

away from the cylinder the middle grip roll is traveling up 
and back through the circular guides, and the hide is released. 
One-half of the hide is fleshed from the center to the end, and 
is then reversed and the other portion is fleshed. The thick 
rubber covering of the bed roll, aided by springs on which its 
bearings are mounted, serves to compensate for varying thick- 
nesses of the stock being worked. Similar springs on the 
bearings of the front grip roll prevent undue compression of 
the thick parts of the hide. 

29. Deliming. — It is essential that the lime or other 
depilating agent should be removed after it has done its work. 



MANUFACTURE OF LEATHER, PART 1 15 

For sole and belting leather, it is only necessary to remove the 
depilating agent, but for soft leather the stock should also be 
brought to an open and flaccid condition, which is accom- 
plished by what is usually spoken of as bating and puering. 
These two terms formerly meant two distinct processes, the 
former term being applied when pigeon or hen manure was 
used, and the latter when dog manure was employed. Today, 
however, the term bating is most generally used and puering 
only spoken of in connection with the manufacture of goat- 
skin into leather. The use of animal excrement in recent 
years has been almost entirely replaced by less objectionable 
materials and that step in the operation placed on a scientific 
basis. 

Ordinary deliming may be accomplished by means of weak 
organic acids or certain chemicals, while bating, puering, or 
drenching must be brought about through fermentation, or 
bacterial or enzyme action. As bating plays only a minor 
part in the manufacture of heavy leather, its consideration 
will be postponed until the processes involved in the production 
of light leather are discussed. Mention should be made, how- 
ever, at this point, of some of the most important chemical 
deliming agents. 

30. Lactic Acid. — In recent years, lactic acid has come 
into quite general use as a deliming agent. About 2 pounds 
of acid are employed for each 100 pounds of stock. This 
acid not only removes the lime, but, if added to the amount 
mentioned, has a tendency to plump the hide, which is very 
desirable in the production of soles. 

31. Formic Acid. — Formic acid comes to the tanner 
as a 60 per cent, solution and is preferred by many on account 
of the rapidity of the action. Like lactic acid, it is also a 
strong plumping agent. 

32. The common practice in heavy leather is, after flesh- 
ing, to wash the stock in running water and then place it in 
the cold pool over night, when the subsequent operations are 
carried out. 



16 MANUFACTURE OF LEATHER, PART 1 

33. Plumping: tlie Hides. — In making sole leathet^ 
where weight is desired, it is advantageous to secure a good 
degree of plumpness before the hide reaches the liquors that 
really do the tanning. By plumping is meant the swelling 
of the cells and the distension of the pores of the hide, so that 
the entrance of the tanning liquor is facilitated. . If the hide 
becomes too plump, hard, brittle leather results ; hence, it is 
very essential that the proper degree of plumpness is attained. 

The plumping is done by acids that are either formed in 
the tan liquors or are added to them. The natural acids 
formed in a vegetable tan liquor are mostly lactic and acetic. 
All of them are of fermentative origin, formed by the decom- 
position of the sugars constituting a part of the non-tannins 
of the bark. The absence of the requisite amounts of non- 
tannins in the liquors will thus cause a scant supply of plumping 
acids. For this reason, several so-called sweet tanning agents 
are unfitted for tanning heavy leathers, unless they are mixed 
with other liquors rich in non-tannins. 

Quebracho extract is a liquor in which the proportion of 
the tannins to the non-tannins is so great that acid is slowly 
formed, and a quick tannage is secured but the leather is not 
well filled or nourished. If quebracho is mixed with some 
liquor with a large non-tannin content, this difficulty is removed. 
The extracts made from oak or chestnut woods are great acid 
makers because of their high percentage of non-tannins. 

34. Methods of Obtaining- Plumping- Acids. — In a 

well-regulated bark yard, the acid formed will be in the proper 
proportion to the tannin in the liquor, and there is no need of 
the addition of plumping agents. It sometimes happens, during 
the cold seasons of the year or when a yard is starting up after 
an extended shutdown, that the acid is deficient. 

Various methods are employed in order to help the formation 
or increase the supply of acid. Crude molasses is sometimes 
added ; a mixture of old cheese, molasses, or glucose, and some 
substance containing nitrogen, as ammonium nitrate, will 
stimulate the production of lactic acid. Commercial lactic, 
acetic, and formic acids are all used for plumping purposes. 



MANUFACTURE OF LEATHER, PART 1 17 

The increasing percentage of extracts used for tanning is 
gradually causing the tanner to provide means for the devel- 
opment of acid in his yard, and eventually in every tannery 
the plumping acid will have to be added to the liquors in 
the form of organic acids, or grown in the liquors by the 
addition of ferments, or by the use of acid-forming tanning 
materials. 

35. It sometimes happens that too much acid is formed 
in the yard. The reason for this is not easily determined. 
It may be due to the season or the weather ; it may be caused 
by the method of leaching, the nature of the water supply, or it 
may be due to other causes seemingly too insignificant to 
produce such an effect. A tannery where the bark is closely 
leached will have more acid in the yard than the tannery 
where there is less regard for economical practices in the leach 
house. A very soft water or a peaty water will help acid 
production. 

A yard with too much acid is harder to handle than a yard 
with too little acid. It requires close watching to prevent the 
production of hard leather inclined to crack and a consequent 
heavy financial loss. This condition of the yard may be only 
temporary, or it may be a permanent one. In correcting too 
great acidity, the handlers, or rockers, that first receive the 
green stock should receive the first treatment. Dilution with 
weak sweet liquor, or even with water, will help their con- 
dition. Sodium carbonate added to them will, of course, 
neutralize the acid, and soften the leather hardened by the 
excess of acid; but care must be taken as to the amount 
added, for too much sodium carbonate will make the stock 
too soft. 

The addition of an antiseptic, as corrosive sublimate or 
carbolic acid, will stop the formation of acid, but will not 
lessen its amount. The former is the better antiseptic to use, as 
carbolic acid sometimes tends to darken and spot the leather. 
Since the antiseptics do not decrease the amount of actual 
acid present, they are best used in the yard vats to retard the 
development of acid in that quarter. 



18 MANUFACTURE OF LEATHER, PART 1 

36. In a properly managed sole-leather yard, where bark 
liquors are used, deficiency or excess of acid is unusual. Some 
tanners pay no attention to this matter, depending on acids 
introduced into the first liquors for plumping. Commercial 
acetic and lactic acids are commonly used, and while they 
accomplish the end for which they are put in, they are unneces- 
sary in a sole-leather yard, where natural means will generally 
furnish the acid required. 

Where the commercial acids are used, continual vigilance 
must be exercised in paying attention to their strength and 
the amounts to be used; otherwise, the hides will not be 
uniformly plumped and the leather will show a corresponding 
non-uniformity of texture and fineness. With certain classes 
of hides used in making a special class of sole leather, sulphuric 
acid is used for plumping. The use of this agent will be 
discussed in the description of the manufacture of this leather. 

37. The plumping is done in handlers^ or rockers, which 
are vats containing liquors that have been weakened by usage 
and are well soured. The acids present effect the plumping, 
and the small quantity of tannin in the liquors serves partly 
to tan the exterior portions of the hides. To equalize the 
action of the liquors in these vats, the hides are handled, or 
rocked, so that all portions of the hide come in contact with 
the hquor, and the liquor itself is constantly in motion. 

The handlers, or rockers, are generally arranged in sets of 
a number of vats varying in strength. In handling the hides, it 
was formerly the custom to lift each hide from the vat and 
throw it into the next vat in the set, this process continuing 
through all the vats in the set. It is customary now to tie 
the hides one to the other, and by means of a hand reel the 
continuous string of hides is moved from one vat to the 
other. The hand reel is a wooden-stripped cylinder mounted 
on a stand about 4 feet high and turned by means of a crank. 
In operation, the reel is placed between two vats, one man 
turning the crank while another starts the string of hides 
over the reel and then arranges them in the vat that receives 
them, the friction of the hides on the reel carrying them along. 



MANUFACTURE OF LEATHER, PART 1 19 

Handling by rockers is done by means of a wooden frame 
hung by pivots in the center of the top of the vats, so as to 
give a dipping movement of 6 to 8 inches to each end of the 
frame. The hides are hung over sticks placed across the 
frame. Motion is imparted to the frames of the rockers by 
beams connected with overhead shafting. By this means all 
parts of the hide are kept in contact with the liquor which is 
well agitated. This end is also attained in some tanneries 
by hanging the hides in the vats and agitating the liquor 
by means of an air pump, which supplies air to the bottom of 
the vat. The air bubbling up through the liquor keeps it 
in motion. 



SOLE-LEATHER MANUFACTURE 

S8. Methods of Tanning. — The simplest and most 
typical methods of tanning are those used in making sole 
leather. The tanning of other bark-tanned leathers is accom- 
plished mainly by variations of these methods. For this reason, 
a discussion of the various processes of tanning in the manu- 
facture of sole leather will precede the description of processes 
for the tanning of the skins used in the production of more 
delicate leathers. 

The system at present pursued in the tannage of sole leather 
is the result of an evolutionary process depending on the 
selective ability of the tanners themselves. Few scientific 
discoveries have helped them, and the basic principles 
of their art have only recently received attention. This 
state of things is due to several causes : In the first place, 
in an art that has attained a high degree of perfection through 
the endeavors of generations of practical workers, we 
are apt to rest with the results achieved without questioning 
the principles involved. In the second place, the raw mate- 
rials, hide and tannin, being organic bodies of an unknown, 
or at least of a very complex, nature, there was limited foun- 
dation for theories of their natural interactions until more 
knowledge of them was obtained. The field for applied 
research is very promising, however, and much has been done 



20 MANUFACTURE OF LEATHER, PART 1 

in recent years to place this branch of the industry on a 
scientific basis. 

39. Sole leather is always sold by weight, and the cost 
of the hide is from 50 to 70 per cent, of that of the finished 
product. The object of the tanner is to make as many pounds 
of leather from a given weight of hides as he can possibly 
produce. His degree of success in this is technically known 
as gain. In the case of green-salted hides, a large percentage 
of the hide, as it is bought, consists of water and salt and such 
impurities as dirt, dung, and blood, so that 100 pounds of 
green-salted hides will only make from 60 to 80 pounds of 
finished leather. The gain would be spoken of as a gain of 
from 60 to 80. Dry hides contain practically nothing but dried 
hide substance, and 100 pounds of this class of hides will make 
from 150 to 185 pounds of leather, the gain in this case being a 
gain of from 50 to 85. 

With green hides, the gain is the amount of leather made 
from 100 pounds of hides ; with dry hides, the gain is the 
amount of leather made from 100 pounds of hides, less 100. 

40. Vegetable tannage is to a certain extent, no doubt, 
a chemical process, but after the final chemical reaction between 
the hide and the tannin has taken place, the product is capable 
of a further absorption of tannin ; the point at which chemical 
reaction ends and physical absorption begins, has not been 
determined. Suffice it to say, that sole leather may contain 
from 20 to 50 per cent, of tannin, and yet in all cases it may 
be thoroughly cured and perfectly tanned. There is, however, 
a minimum limit at which hide treated with tannin is leather, 
and this limit is the satisfaction of the purely chemical affinity 
of the hide for tannin. 

The whole process is an economical one ; the tannin does 
not change materially while in solution, and it is almost com- 
pletely recovered from the tan liquors by the hide during the 
process of tanning. With vegetable tannage, labor costs are 
low, the only disadvantage being the time consumed and 
consequent loss of interest on the money invested in the 
process. 



MANUFACTURE OF LEATHER, PART 1 21 

41. There are three general varieties of sole leather made 
in the United States, the names given them indicating the 
bark used in tanning. They are oak, hemlock, and a com- 
bination of both, known as union. Each of these classes of 
leather has special modifications represented by special grades 
of leather. The greater part of the sole leather made in the 
United States is tanned by hemlock bark. European prejudice 
against this leather has been removed and immense quantities 
are annually exported. Hemlock leather is produced by two 
methods of tanning — acid and non-acid. Some slaughter 
hemlock is also made, but this forms only a small percentage 
of the output. 

42. Oak Leather. — Leather made from hides tanned 
with oak bark is distinguished by its color and texture. Oak 
bark gives a deposit, or bloom, of ellagic-tannic acid on the 
leather, and oak leather is known as scoured or Texas, 
depending on the removal of this bloom. 

The hides used are green and generally of native slaughter. 
The Texas hides are usually from range cattle, and are made 
mostly into unsecured leather; those hides which are not 
branded or have only small brands are used for scoured leather. 
South American hides make a good grained scoured leather 
and are in demand for men's shoes of the highest grade. 

The hides are placed in the soaks for about 3 days, but 
the time may be shortened by using warm water and a loss 
in hide substance saved thereby. The water in the soaks is 
changed with each pack of hides. Some tanners remove the 
hides after the first day's soaking and replace the dirty water 
with fresh. 

The hides may be fleshed after soaking or they may be put 
in the limes and the fleshing and unhairing done after they 
leave the limes. Different tanners have different methods of 
liming this class of hides. Some leave them in the limes as 
long as 5 days, while others complete the liming in 2 days, 
handling the hides continually and using a lime-sulphide mix- 
ture. It is claimed that a warm bath of, say, 100° to 110° F. 
given to the hides the night previous to unhairing, is beneficial. 



22 MANUFACTURE OF LEATHER, PART 1 

After soaking, the hides may be split along the spine line 
into two sides, or the splitting may not occur until after liming, 
and in some tanneries the whole hide is tanned. 

After unhairing and fleshing, it is the custom in some 
tanneries to bate the stock. With the amount of acid usually 
present in an oak tannery, however, this is unnecessary and 
is the exception rather than the rule. The hides are usually 
placed in a vat of clear water and permitted to remain there 
overnight. The hides are then suspended in the rockers, and 
the real tanning begins. 

43. The rocker vats are in complete sections, piped so 
that liquor from the bottom of one vat is delivered to the top 
of the next. As liquor is supplied to the head, or strongest, 
rocker vat, it gradually works around through all the vats, 
being weakened in each by the presence of the hides, until it 
reaches the weakest, or tail-rocker, vat, from which it flows 
to waste. The stock is hung in this tail-rocker vat, and is 
here constantly rocked in contact with the liquor coming from 
the next vat, which gradually becomes stronger until it is 
receiving the strongest liquor and has become the head- rocker ; 
the stock is then removed and is ready for the lay-away vats. 

The object to be attained with the rocker liquors is the 
removal of the lime remaining in the grain (it being neutral- 
ized by the organic acids in the liquor), the swelling of the 
hide, and the setting of the color. The quality of the leather 
is determined by the work done in the rockers and handlers, 
according as the plumping, coloring, etc., is properly done. 

The liquor used in the rockers should be old, mellow, and 
not strong. The strength of the liquor is regulated by the num- 
ber of pits in use, so that the green hides should have sufficient 
acid to purge them of lime and properly start the plumping. 

44. From the rockers the hides are taken to the main 
tanning yard, where the lay-away vats are located. These 
vats are generally 9 feet long, 7 feet wide, and 5J feet deep. 
In these, the hides are laid out flat, one by one, and a thin 
layer of ground oak bark sprinkled over each hide. This bark 
should not be ground too fine, or the weight of the pack will 



MANUFACTURE OF LEATHER, PART 1 



cause the hides to settle together too much and the circulation 
of the liquor will be prevented, thereby destroying one of the 
purposes of the bark, and ultimately resulting in imper- 
fectly tanned leather. Each layer is treated in the same way, 
fresh tan or bark being used in each case. 

After laying away has begun, the tanning is conducted on 
lines peculiar to the individual tanner. Each man has his own 
ideas as to how much liquor the hide should receive and under 
what conditions. In general, the hides are allowed to remain 
in a lay-away until the liquor in that vat is sapped. The hides 
are then removed, the liquor run off, and stronger liquor used 
after repacking the hides, as before. 

TABLE I 

LAYER SCHEDTJL.E FOR OAK-BARK TANNING 



Layer 


Time in Layer 
Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Approximate 

Percentage of 

Tannin 


First 


8 
12 

i6 

32 


34 

38 
38 

40 

48 


4.00 


Second 


4-2^ 


Third 


4-25 


Fourth 


4-75 


Fifth 


5-75 ■ 





Each pack of hides is laid away from four to seven times, 
according to the theories and judgment of different tanners, 
the whole operation of laying away extending over a period 
of from 3 to 5 months. These successive lay-aways are called 
layers and are known as first, second, third, etc., layers, accord- 
ing as they represent the first, second, or third lay-away that 
the hides have received. 

45. Tanners diifer not only as to the number of layers 
that oak leather should receive, but also regarding the tem- 
perature and strength of the liquor on these layers. For 
example, the schedule shown in Table I is in effect in a large 
tannery where oak-bark tanning is employed. 



24 



MANUFACTURE OF LEATHER, PART 1 



46. In another successful tannery where the oak-bark tan- 
ning process is used, six and sometimes seven layers are given. 
The temperatures of the various layers are also kept well up, 
and if it is necessary to tan the hides in a shorter period, these 
increased temperatures, with proper regard for the strength 
of the liquors, will produce the desired effect. Only a few 
years have elapsed since the use of warm liquors in the yard 
was inaugurated, and they have not been well received by all 
tanners. The schedule followed in this yard is given (in 
Table II. 

TABLE II 



LAYER SCHEDULE FOR 


OAK-BARK TANNINa WITH WARM 
LIQUORS 


Layer 


Time in 
Layer 

Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Temperature 

Degrees 

Fahrenheit 


Approximate 

Percentage of 

Tannin 


First 

Second .... 

Third 

Fourth .... 

Fifth 

Sixth 


8 
II 
i6 

25 

34 
48 


34 
38 

35 
40 

44 
50 


70 

75 
80 

90 

100 

no 


4.35 
5.00 

4.60 

5.15 
5.80 

6.40 



The time taken for tanning by this schedule is a little longer 
than by the first one given, but the leather seems to be of a 
closer texture, better filled, and of better wear-resisting 
qualities. 

The first-layer Hquor in this yard is an old Hquor — ^the 
sapped fifth layer — and the second-layer liquor is also an old 
liquor — the sapped sixth layer. The other liquors are new, 
sweet liquors made by strengthening oak-bark liquors with 
chestnut-wood extract. 

47. Oiling and Drying tlie Leathers. — When the 
tanning is complete, the sides are taken from the last layer 
and thrown into warm water to clean the grain of sediment 



MANUFACTURE OF LEATHER, PART 1 25 

or fine particles of bark. After rinsing, the sides are piled to 
drain overnight. They are then swabbed with cod oil, or a 
mixture of cod and other fish oils, or a mixture of mineral 
oil and fish oils. The swab used is a piece of sheepskin tanned 
with the wool on. The sides are then hung on sticks or by 
brass catches in the drying loft. 

48. The drying loft is generally located over the vat yard ; 
steam pipes are spread over the loft floor and rest on blocks 
that support the pipes and allow air to circulate around them. 
A slat-work floor over the pipes serves as the floor of the loft. 
Tight windows and ventilators are provided so that the proper 
adjustment of light and ventilation can be maintained. In 
some tanneries, the heat and ventilation are supplied by 
mechanical means, blowers carrying air to the loft and keeping 
the atmosphere in constant circulation. Without proper cir- 
culation the air becomes stagnant among the closely hung 
leather and the damp leather will become moldy. To aid in 
keeping the air in circulation, openings that may be regulated 
as to size are generally distributed around the floor of the loft. 
The same end may also be attained by forcing air into the 
loft at a pressure slightly above that of the atmosphere, thus 
effectually moving any stagnant air. 

The leather is hung over poles whose ends rest on beams, 
or it may be held by an ingenious brass device in which the 
weight of the side causes friction to uphold it. 

49. Rolling' tlie Leather. — When thoroughly dry, the 
sides are taken from the drying loft to the rolling room and 
there brushed with water and made into covered piles. When 
properly tempered, the sides are oiled on the grain side, rolled 
and dried in the loft, and, when dry, are sorted for the market. 
The rolHng of the leather serves to smooth the grain side and 
compress the leather, thus making it firmer. It also puts 
somewhat of a polish on the finished leather. Rolling is 
effected by machinery. 

50. The leather roller is a machine consisting of a 
heavy beam having on its end a polished brass wheel. This 



26 MANUFACTURE OF LEATHER, PART 1 

wheel is about 8 inches in diameter and has a 6-inch face. 
A crank gives to the beam a direct motion, allowing the brass 
wheel to move about 1 foot each way right and left. The 
leather is held under the moving wheel, or roller, on a small 
bed of brass conforming to the arc described by the roller. 
A foot-lever serves to raise this bed and makes the pressure 
of the moving roller Hght or heavy, according to the will of 
the operator. By moving the leather around under the roller, 
all parts of it are finally smoothed and polished. 

51. In some tanneries, the vat sizes of which necessitate 
it, the hides are split into sides as they come out of the soaks 
or out of the limes. Whole-hide tannage is more economical 
as to labor costs in the yard, but side tannage is more economical 
in beam-house work. 

A large, light-colored, and even deposit of bloom on oak 
leather is considered a mark of fine tannage; for some pur- 
poses, the leather is sold with the bloom removed and is then 
known as scoured leather. For this leather, the hides are 
split and rinsed as usual. Then they are scoured by the 
scouring machine, drained, oiled, and dried. After this, they 
are dipped in water, rolled, and dried, and then receive a 
final rolling before going to the sorting room. 

52. Most of the old-style oak sole leather is made from 
hides tanned in the manner just mentioned; but a considerable 
amount of so-called oak leather is also sold that is tanned 
with oak bark and chestnut-wood extract by methods similar 
to those used for tanning non-acid hemlock and union crop 
leather. The leather is bleached, and it is oiled in the wheel 
instead of by hand ; and, except in the matter of tanning 
materials used, the process of tanning is quite different from 
true oak tanning. 

53. Non-Acid Hemlock Tanning-. — In the non-acid 
hemlock process of tanning, the hides are swelled, or plumped, 
by the natural ferment acids in the tan liquors, while in the 
acid process, a solution of sulphuric acid is used to effect the 
plumping. 



MANUFACTURE OF LEATHER, PART 1 27 

54. Treatment of the Hides. — With the non-acid 
hemlock process, the hides used are generally dried South- 
er Central-American skins. They are well soaked and soft- 
ened with the help of the hide mill. It is the usual practice 
to soak the hides from 5 to 8 days ; then they are milled and 
thrown back into water for another shorter period. They 
are then milled again and may receive another day's soaking 
before the tanner considers them soft enough for good results. 
After soaking, they are split along the spine line into sides, 
and the hair is removed by either sweating or liming. After 
the removal of the hair and fleshing, the sides are soaked 
overnight in water and are then ready for the handlers. Limed 
stock is bated in some tanneries, a light bran or hen-manure 
bate being used. Before putting it in the handlers, some 
tanners color the stock by running it for a few minutes in a 
paddle wheel revolving in a vat of acid spent liquor of from 
8° to 12° Bk. 

55. The sides are strung together for handling by tying 
a shank of one to the shank of the next, and the string of 
hides is then dropped into the tail, or weakest, handler vat. 
The handler vats are arranged in continuous sections that are 
so connected that liquor run into the head vat passes suc- 
cessively through the other vats in the section, flowing from 
the top of one vat to the bottom of the next. Hand or power 
reels are placed between each pair of vats so that the string 
of sides may be easily moved from one vat to the other. The 
handler liquors are sapped liquor, generally from the first 
three layers of the lay-away yard ; they are weak in tannin 
and contain the natural plumping acids. The head, or strong- 
est, handler liquors are generally from 14° to 18° Bk., 
and are sapped by the green stock until the tail, or weakest, 
handler liquor becomes of a gravity not much above 8° Bk. 
The strength of the handler liquors depends on the strength 
of the lay-away yard, which is controlled by the method of the 
tanner in charge. The stock is put into the tail-handlers and 
reeled forwards and backwards, perhaps every hour during the 
first 24 hours, and possibly eight or ten times during the sec- 

293—3 



28 



MANUFACTURE OF LEATHER, PART 1 



ond day. This reeling serves to change the position of the 
stock as it Hes in the hquor, plunges the liquor, brings every 
part of the hide in contact with the liquor, and equalizes the 
effect of the tannin and color on the green stock. After the 
first 2 or 3 days in the handler liquor, the stock is reeled 
forwards once every day into a stronger vat until the head- 
handler or strongest handler is reached; and, the handler 
liquors having accomplished the plumping and started the 
tanning, the strings are removed and the stock goes to the 
lay-away yard. Here, the stock receives from five to seven 
layers in liquors of different strength, according to the methods 
in use at the tannery. 

56. A schedule in use at a successful non-acid tanneiy is 
given in Table IH. 

TABLE III 

liAYER SCHEDULE FOR NON-ACID TANNING 



Layer 


Time in Layer 
Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Approximate 

Percentage of 

Tannin 


First 

Second 

Third 


7 
II 

12 

i8 

19 
26 


21 
22 

23 

24 

28 

28 


2.85 

3.60 

3.75 
4.00 

4.00 


Fourth 


Fifth 


Sixth . 





In this tannery the liquors are used at a temperature of 
from 70° to 75° F. on all the layers. The first layer is an 
old liquor that has been sapped by usage on the fifth layer, and 
the second-layer liquor is also old, having been sapped on the 
sixth layer. The third-, fourth-, fifth-, and sixth-layer liquors 
are all sweet liquors made by strengthening leach-house liquor 
with extract. The sapped liquors from the first, second, and 
third layers are used as handler liquors ; the fourth layer 



MANUFACTURE OF LEATHER, PART 1 



29 



sapped is returned to the leach house, and the fifth and sixth 
layers sapped, as just explained, are used for first- and 
second-layer new liquors, respectively. 

The hides are kept in the first-layer liquor for the required 
number of days. The pack is then hoisted, the old liquor 
removed for handler purposes, and the hides placed in the 
second layer. This process of treating the skins to successively 
stronger tanning liquors goes on until the last layer is reached. 
The leather is then finished so far as actual tanning is con- 
cerned. The length of time for each layer is a matter deter- 
mined by the judgment of the tanner, and therefore differs 
with conditions. Theoretically, it would be best to allow a 
pack of hides to remain in a layer until there was no more 
sappage, or taking up, of tannin by the hides. After the 
tannin contents of hide and liquor are equal, months of further 
contact will not put any more tannin in the hide in that layer. 

TABLE IV 

LAYER SCHEDULE FOR NON-ACID TANNING WITH WARM 

IiIQ,UORS 



Layer 


Time in 
Layer 

Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Temperature 

Degrees 

Fahrenheit 


Approximate 

Percentage of 

Tannin 


First 

Second .... 

Third 

Fourth .... 

Fifth 

Sixth 


5 

12 

i8 

20 

24 


2^ 

32 

34 
38 
40 


70 
80 

85 
90 

100 

no 


3-15 
340 
3.60 
4.00 

4.75 
5.00 



57. Use of Warm Liquors. — There is some prejudice 
against the use of warm liquors in a tan yard, but if the proper 
limit of heat is not passed, the results seem to be beneficial. 
By the use of warm liquors, the length of time on the first 
layers is shortened and stronger liquors used. In one tannery 
where warm liquors are used, six layers of liquor are given 



30 MANUFACTURE OF LEATHER, PART 1 

to the stock. The schedule of this tannery is shown in 
Table IV. 

The liquors at this tannery are made up as follows: The 
first-layer new liquor is the sapped liquor from the fifth layer ; 
the second-layer new liquor is made by taking equal portions 
of the sixth-layer sapped liquor and liquor from the leach 
house. The third-, fourth-, fifth-, and sixth-layer new liquors 
are made by strengthening leach-house liquors with chestnut- 
wood extract. 

The temperatures on the different layers are adhered to 
within a range of 5 degrees either way. With these warm 
liquors, the duration of the tanning process may be shortened, 
but an increased period does not harm the stock. 

With the old process of tanning, the leather, after coming 
out of the last layer, is thrown into a pool of water to remove 
the sediment that has accumulated on the surface of the 
leather. This is also frequently accomplished by placing the 
leather in a drum with water and revolving it for a few 
minutes. 

58. Bleadiing. — After the rinsing process, the leather 
is piled to drain and then bleached. The bleaching to which 
sole leather is usually subjected is not really a bleaching 
process, because the excess of tannin on the surface of the 
leather, which lightens the color of the stock and also makes 
it less liable to crack, is simply dissolved and removed. The 
bleaching consists in dipping the leather into an alkaline bath 
that dissolves and removes the excess tannin, then into an acid 
bath that neutralizes any soda remaining on the leather, and 
finally into water to remove the remaining acid. For con- 
venience in handling the leather, the three vats are placed in a 
row, and the leather, hung on sticks supported on a frame, goes 
into one vat for the desired time. Then, the frame is raised 
and the leather drained, after which it is put into the next vat. 
This process is continued until the bleaching is completed. The 
time necessary for the reaction that takes places in each bath is 
utilized by the workman in unloading a frame of bleached 
leather and in loading a frame of leather ready to be bleached. 



MANUFACTURE OF LEATHER, PART 1 31 

Sodium carbonate, as sal soda or as soda ash, is the alkali 
generally used, because it is the cheapest ; and, for the same 
reason, sulphuric acid is the acid always used. The tanner 
regulates the strength of the bleach by varying the quantity of 
soda ash or sal soda (and accordingly the acid), the strength 
depending on the color desired. 

59. After bleaching, the leather is hung or piled to drain 
and to dry off slightly before oiling. Hand oiling is now rarely 
employed, the majority of tanners applying the oil in the oil 
wheel. The oil wheel is simply a revolving wooden drum 
fitted with a removable door, and hollow axles through which 
the oil is pumped. The oil used is either cod oil, winter- 
pressed fish oil, or mineral oil, or mixtures of these oils. 
Many tanners adhere to the use of cod oil, but a good grade of 
fish oil from which the sediment has been removed by pressing 
while chilled — or what is known as winter-pressed oil — will 
give the same results as cod oil and is cheaper. The mineral 
oil is cheaper than either fish or cod oil and gives satisfactory 
results when mixed with higher-priced oils. 

GO. The color of sole leather is one factor that determines 
its market price, and although it seems the height of folly to 
demand a qualification that does not affect the quality of a 
product, yet the extent to which this demand for a good color 
has been carried has resulted in recourse to means of supplying 
the demand. In the hands of some tanners, these means have 
been used for the accomplishment of an end other than the 
one originally intended, and as a result, there is considerable 
cry about the adulteration of American sole leather. Leather 
dried in the rough, unless so heavily bleached as to remove too 
much of its weight, is liable to become dark at certain points 
on the side. The addition of a small amount of a mixture of 
glucose, or grape sugar, and sulphate of either magnesium or 
sodium, to the leather, serves to overcome this tendency and 
results in a leather that dries easily and finishes bright. In 
addition to these benefits, the leather thus treated will have 
firmer flanks and bellies, and it remains in better physical con- 
dition, so, that it can be cut and worked more readily. The 



32 MANUFACTURE OF LEATHER, PART 1 

amounts of the materials necessary to produce these results in 
a side of leather are so small that their use for this purpose 
cannot be called an adulteration. The ease with which these 
materials can be added, however, has, of course, resulted in the 
production of some cheap, adulterated leather. 

61. The glucose and salts are generally added with the 
oil in the oil wheel. When the leather is in the proper con- 
dition for oiling, it is thrown into the oil wheel and J pound 
of Epsom or Glauber salts and J pound of glucose for each 
side, are also thrown in. The door is then put on and clamped, 
the oil pumped in through the hollow axle, and the wheel 
revolved from 30 to 60 minutes. At the end of this time, the 
revolving wheel has caused the tumbling leather it contains to 
absorb oil and other materials added, and the leather is 
removed on trucks to the dry loft, where it is hung on sticks 
and dried. 

For the first day or so after lofting the leather, drying 
progresses without steam or light, but with proper ventilation. 
The temperature of the loft is then gradually raised until 
the drying is complete. This process requires from 10 to 
25 days, depending on weather and local loft conditions. 

After the leather is thoroughly dried, it is taken down, dipped 
into warm water, and piled down to sammie, or to equalize, 
for 1 to 2 days. Warm water is then sprinkled on the grain 
side, care being taken that every portion is wet. Then the 
leather is swabbed with cod or other fish oil, after which it 
goes to the rollers for a first rolling. After the first rolling, 
the leather may be hung and thoroughly dried before the 
second rolling, or it may be piled and second-rolled while in a 
comparatively wet condition. After second rolling, the leather 
is hung by one end in the finished-leather loft and, when dry, 
is sorted and graded for market. 

62. Wheeling or Extracting. — In most of the tanneries 
of the present, the time of tanning in the yard has been mate- 
rially shortened and the weight that the hide does not receive 
in the yard is given it by zvheeling with the tanning solutions. 
The wheels used for this purpose are from 8 to 10 feet in 



MANUFACTURE OF LEATHER, PART 1 33 

diameter and from 5 to 6 feet wide ; they are mounted on 
trunnions and revolved on a horizontal axis by a pinion geared 
to teeth set around the perimeter of the wheel. A removable 
tight door secured by clamps provides for the loading and 
unloading of the wheel, and tannin solution is pumped into the 
wheel through its hollow axle. 

The methods of wheeling and methods of actual tanning 
vary to the same extent. Each tanner has his own ideas as 
to the treatment of the stock before and after wheeling, as to 
the amount, temperature, character, and strength of the tanning 
solution, and as to the duration of the wheeling. The char- 
acter, size, and the condition of the leather all determine the 
kind of treatment to be used, and the tanner's experience tells 
him what treatment will produce the best results under given 
conditions. 

OS. After the yard tanning is complete, the leather is 
thrown into water to wash off any adhering sediment, and it 
is then hooked out and goes to the wringer, which is a mam- 
moth clothes wringer provided with felt-covered brass rolls. 
The leather is fed into the wringer and comes out with the 
excess of moisture removed. As the sides of stock come from 
the wringer, they are piled on trucks, taken to the wheels, 
and thrown in. The door is put on, clamped in place, and 
the wheeling materials pumped into the wheel. The materials 
used include all kinds of tanning liquors, such as chestnut 
wood, oak bark, hemlock bark, quebracho, sumac, quercitron, 
and other liquors, varying in strength from 100° Bk. to the 
undiluted extract running from 42° to 50° Twaddell (210° to 
250° Bk.). The temperature at which these materials are 
used varies from 100° to 160° F., according to the practice 
of the tanner. After the leather and wheeling material have 
been put into the wheel, the power is applied and the wheel 
makes from 15 to 20 revolutions per minute, the speed varying 
according to the diameter. The revolution causes the leather 
to roll and fall within the wheel, and, being in constant contact 
with the tanning solution, the latter is mechanically absorbed 
and incorporated into the leather. 



34 MANUFACTURE OF LEATHER, PART 1 

64. The completeness with which the wheeling material 
is absorbed depends on the character, size, and condition of 
the stock, and obviously on the amount of solution added to 
the wheel. The amount varies from a quantity of solution that 
represents 1 pound of solids to the side to a quantity repre- 
senting 4 pounds to the side. The duration of the wheeling 
varies from 45 minutes to 2 hours, and on the expiration of 
the required time, the wheel is stopped, the door removed, and 
the contents of the wheel removed to a truck. From the 
wheel, the stock may be piled in low, covered piles, it may be 
hung over sticks in a dark, cool place, or it may be laid away 
in strong-liquor vats. This treatment is for the purpose of 
allowing the mechanically added material to permeate the 
leather thoroughly and uniformly. After piling, hanging, or 
laying away the stock for the desired period, it is taken to the 
bleach room. From this point until the leather is finished, 
the operations are the same as for leather that has not been 
wheeled. 

65. Acid Hemlock Leather. — By acid hemlock leather 
is meant a variety of hemlock sole leather that has been 
plumped by means of sulphuric acid. Other kinds of sole 
leather are made from hides that are plumped by organic acids, 
which are either naturally present in the liquors or have been 
added to them. The sulphuric acid causes an abnormal dis- 
tension of the pores and swelling of the tissues. 

Most of the acid hemlock leather is made from dried hides ; 
that which is made from green hides is known as slaughter 
hemlock sole. The process of manufacture is the same, except 
that the hides, being green, are generally depilated by means of 
lime instead of by sweating. The dried hides are largely of 
South American or of Asiatic origin, this being a very popular 
method of tanning the Chinese Buffalo hides. 

The hides are soaked, limed or sweated, depilated, and 
fleshed in the usual manner and then soaked in clear water. 
After this they go into a weak tanning liquor. This liquor 
exerts its slightly astringent effect on the hides, and they are 
somewhat colored by the bath. 



MANUFACTURE OF LEATHER, PART 1 35 

66. Plumping- Witli Sulpliuric Acid, — After the 
treatment just mentioned, the hides are put into a .1 to 
.3 per cent, solution of sulphuric acid and kept there until the 
swelling has progressed to the desired stage. They are then 
ready for the tan yard. 

Because of the abnormal plumping by the sulphuric acid, 
the hides can safely be put into strong liquors. In the other 
processes of sole-leather tanning, the hides receive weak-liquor 
treatment, the strength being gradually raised until the maxi- 
mum is attained. In this branch of the industry, there are no 
true rockers, or handlers. The only tannin treatment they 
receive before going to the first-layer liquor is the slight 
coloring from the weak tanning somtion before plumping. 

After plumping, the hides go to the first-layer liquors for 
the time required for this layer. The first-layer hquor in an 
acid tannery soon becomes impregnated with sulphuric acid 
and sulphates, and must then be discarded. The free 
sulphuric-acid content is generally not very high in this 
liquor, but there is sufficient to interfere with the tanning 
action. The liquors become very dense and the proportion 
of tannin to the total solids is low, so that there is little 
sappage to be obtained. The gravity of this first-layer sapped, 
or run-to-creek, liquor is from 18° to 25° Bk. and it will contain 
from .8 to 1.5 per cent, of tannin. 

A great deal of thought has been spent in trying to devise 
some method of saving the tannin and to avoid the necessity 
of running this strong filth-bearing liquor into, and thus 
contaminating, a stream. The removal of the sulphates by 
precipitation with barium chloride and subsequent settling has 
also been proposed. In some tanneries, the practice is to run 
this liquor over a spent leach of tan bark ; this process removes 
the free acid as well as some of the solid impurities. 

67. As in the case of the other sole-leather tanning 
processes, there are various systems in use in this branch of 
the industry. There is a little more latitude here, however, 
than in oak or non-acid hemlock tanning, the first-layer liquor 
being used in many strengths by different tanners. The liquors 



36 



MANUFACTURE OF LEATHER, PART 1 



are made by combining bark and extract liquors according to 
the latest practice of all sole-leather tanners ; from five to 
seven layers of liquors are used, either cold or warm. A 
schedule of strengths in a cold-liquor tannery is given in 
Table V. 

The first-layer liquor is a sixth-layer liquor that has been 
sapped by a tanned pack. All the other liquors are made 
from leach-house liquor or leach-house liquor strengthened 

TABLE V 

LAYER SCHEDULE FOR ACID HEMLOCK TANNING WITH COLD 

LIQ,UOR 



n 



Layer 


Time in Layer 
Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Approximate 

Percentage of 

Tannin 


First 


8 
II 

15 

24 
24 

27 


38 
40 

42 
42 

44 
48 


3.60 

3-90 
4.20 

4.50 
5.00 

540 


Second 


Third 


Fourth 


Fifth 


Sixth 





with chestnut-wood extract. The sapped first-layer liquor is 
run to waste, and the other sapped liquors (with the exception 
of the sixth layer) are returned to the leach house. 

68. In Table VI is given the schedule followed in a 
warm-liquor tannery using seven layers of liquors. 

In this tannery, the first-layer liquor is a sixth-layer liquor 
that has been sapped, the second layer is a seventh-layer 
liquor that has been sapped, while the other liquors are leach- 
house liquors made by building up all sap liquors but the first 
and seventh, which are run to waste and to first-layer new, 
respectively. 

After the leather has been tanned in the yard, it is further 
treated by the methods described under the head of Non-Acid 
Hemlock Tanning. 



MANUFACTURE OF LEATHER, PART 1 



2>7 



69. Acid slang-liter sole leather is made from green 
hides, the hair being removed by either liming or sweating. 
When the hides are Hmed, a bate is sometimes used in the 
production of this variety of leather, but otherwise the liquors 
and operations are the same as in the manufacture of the 
regular acid hemlock leather. The use of sulphuric acid as a 
plumping agent results in the production of a firmer leather. 
The action of the acid is much more energetic on sweated 
hides than on limed stock, because in the limed-stock treatment, 
part of the acid is neutralized. Therefore, in the regular acid 
process, care must be observed as to the degree of plumpness 
attained. 

TABLE VI 

LAYER SCHEDULE FOR ACID HEMLOCK TANNING WITH WARM 

LiaUOR 



Layer 


Strength of 
Liquor 

Degrees 
Barkometer 


Time iu 
Layer 

Days 


Temperature 

Degrees 

Fahrenheit 


Approximate 

Percentage of 

Tannin 


First .... 




7 


27 


65 


2.50 


Second . . 




9 


29 


75 


2.80 


Third . . . 




12 


30 


85 


3.00 


Fourth . . 




13 


32 


90 


3.20 


Fifth ... 




15 


34 


100 


340 


Sixth ... 




19 


34 


105 


3.80 


Seventh . 




28 


36 


no 


4.10 



70. Union Leatlier. — The combination of hemlock and 
oak barks gives a very serviceable leather known as union 
sole leather, which has a better texture than hemlock-tanned 
leather, is tougher, and has a color somewhat like that of oak- 
tanned leather. There is probably more variation in the 
processes of making this leather than in making other kinds 
of sole leather. 

Color is all-important, and many methods for its improve- 
ments are being used. Some go back to the leach house to aid 
color, and sacrifice tannin there in order to have very pure 



38 MANUFACTURE OF LEATHER, PART 1 



liquors, which will give the leather a bright, clean shade. An 
illustration of the wide difference in union methods may be 
seen in the fact that in some union tanneries the first-layer 
liquors are as low as 8° Bk., while in others they run as high as 
25° Bk. These liquors are, however, not of the same purity. 
The 8° liquor will show a higher proportion of tannin to the 
total solids than the 25° liquor, but, aside from this, the tannin 
strength of the 25° liquor is greater than that of 8° liquor. 
In tanneries where strong liquors are employed, considerable 
oak or chestnut-oak extract is used, the upper layers being 
strengthened, and the texture and color improved thereby. 

71. Most of the union leather made is cropped; that is, 
the bellies and shanks are cut from the sides, making the prod- 
uct rectangular. The crop leather thus made commands a 
higher price than union side leather, because much waste is 
avoided when it is cut into soles. The bellies, shanks, etc. are 
sold for scrap leather for inner soling, etc. A good quality 
of cut soles is made from union leather, and the method of 
selling these cut soles determines the method of tannage in 
some tanneries. A certain number of soles will be cut from 
several tannages of leather, and the leather that will give the 
largest number of soles to a given weight of leather is gen- 
erally the best seller, if other considerations, as color, firm- 
ness, and texture, are equal. This causes tanners to endeavor 
to produce a light crop leather of a good color, strength, and 
closeness of texture. These qualities can be obtained by the 
use of very pure Hquors of low barkometer degree. Since 
purity of the liquor is secured at the expense of leaching, it is 
really questionable whether this method of tanning pays. 
More leather can be made from a ton of bark by this process, 
but the actual gains will not be so great as when a heavy, 
well-filled leather is produced. 

72. Green-salted hides are used for making union leather. 
They are well soaked, Hmed, unhaired, fleshed, and placed 
in clear water overnight, after which the hides go into the 
rockers. According to the method of tanning in use, the 



n 



MANUFACTURE OF LEATHER, PART 1 



39 



rocker liquor and all other liquors vary in strength. After 
coming from the rockers, the leather is cropped in some tan- 
neries, while in others it is tanned and finished as side leather 
and then cropped. When cropped out of the 'rockers, the heads 
and bellies are strung together and thrown on top of the 
regular leather in the lay-away vats. From the rockers, the 
sides go into the lay-away yard ; from five to seven layers are 
given, using oak bark on every layer. The oak bark is ground 
fine, but not fine enough to prevent the circulation of liquor 
between the sides in the vats. After use in the lay-aways, 
the bark is sent to the leach house and leached with the 
hemlock bark for the union liquors. It is generally placed on 
the bottom of a leach, the hemlock bark being run in on 
top of it. 

TABLE VII 

liAYER SCHEDULE FOR UNION TANNING WITH COLD LIQUOR 



Layer 


Time in Layer 
Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Approximate 

Percentage of 

Tannin 


First 


6 
10 
lO 
12 

15 

25 


14 

i6 
i8 

20 

25 


2.25 
2.50 

2.75 
3-25 

3-75 

4.50 


Second 


Third 


Fourth 


Fifth 


Sixth 





73,. A schedule of layers and liquors in a tannery using 
cold, weak liquors is shown in Table VIL 

The leather from this tannery is of a very beautiful color, 
light in weight, and quickly tanned. The sapped liquors are 
strengthened by returning to the leach house, and no extract 
is used. The liquors are very pure; in fact, some of them 
are of such purity that 65 per cent, of the total solids are 
tannins. With this purity, the spent tan, of course, shows con- 
siderable tannin, the amount sometimes running as high as 
2.25 per cent. The sides are completely tanned here and are 



40 



MANUFACTURE OF LEATHER, PART 1 



cropped after finishing. The yard operations are carried on 
in the usual manner, and the sapped upper layers which return, 
to do duty as lower layers, are strengthened in the leach 
house. 



74. To show the difference in methods, the schedule of 
another cold-liquor tannery is given in Table VIII. 

This tannery is a typical, modern, union crop tannery, no 
oak bark, excepting that used for dusting between the leather 
in the lay-aways, being employed. The union color is made 
by combining hemlock-, quebracho-, and chestnut-wood liquors, 
the resulting leather having a good color and all the physical 

TABLE VIII 

LAYER SCHEDUI.E FOR UNION TANXING WITH COI^D I^I^UOR 



Layer 


Time in Layer 
Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Approximate 

Percentage of 

Tannin 


First 


7 
II 

2.2. 


i6 

21 
21 

23 

25 


2.50 

3-25 
3-25 
3-75 
4.50 


Second 


Third 


Fourth 


Fifth 



characteristics of union leather. The fifth-layer sapped liquor 
is used for the first-layer new liquor, the fourth-, third-, 
second-, and first-layer sapped liquors being used as rocker 
liquors. The new liquors (except first layer) are made by 
strengthening the leach-house liquor with equal portions of 
quebracho- and chestnut-wood extract. 

75. A warm-liquor tannery using strong liquors and con- 
siderable extract had the schedule given in Table IX. 

Six layers were in use at the tannery, although ordinarily 
but five are given. This tannery makes rather heavy leather, 
of a good color, and the bark used is well leached. Extract 



MANUFACTURE OF LEATHER, PART 1 



41 



is used for strengthening the Hquors, some of which are 
returned to the leach house for strengthening. 

76. The use of weak or strong yard Hquors depends on the 
expected finishing treatment of the leather. In a tannery using 
wheels for the mechanical addition of tanning material to the 
leather, the yard liquors are generally weaker in barkometer 
strength and higher in purity than in yards pursuing the old 
methods of union-leather tanning. After the yard tanning, 
the leather is cropped, provided this operation has not been 
performed previously. It is then finished by rinsing, bleach- 
ing, oiling, drying, and rolling, as has been previously 

TABLE IX 

liAYER SCHEDULE FOR UNION TANNING ^WITH WARM L.IQUOR 



Layer 


Time in 
Layer 

Days 


Strength of 
Liquor 

Degrees 
Barkometer 


Temperature 

Degrees^ 
Fahrenheit 


Approximate 

Percentage of 

Tannin 


First 

Second .... 

Third 

Fourth 

Fifth 

Sixth 


7 
II 

14 

20 

33 


22 

24 
26 
28 

31 

34 


65 

75 
8o 

90 

100 

105 


3.00 

3-50 
4.00 

4.60 

5.00 

5.60 



described; or, if preferred, it may be wheeled with tanning 
material, as described under the head of Non-Acid Hemlock 
Tanning, and then finished in the regular manner. Union crop 
leather is generally rolled only once, the gloss of hemlock 
leather not being required on union leather. 

77. Quick Sole-Leatlier Tannag:e. — To tie up the 

immense amount of money that is represented by hides in 
process of tanning by ordinary methods of making sole leather, 
requires either a large working capital or excellent credit. In 
either case, the interest on this tied-up money is a considerable 
item in the cost of tanning. For this reason principally, quick- 



42 MANUFACTURE OF LEATHER, PART 1 

tannage methods have been and are being devised with the 
hope of producing a leather as good as the long-tanned product 
and without the necessity of employing as much unproductive 
capital as the manufacture of the latter entails. 

Many methods of quick tannage have been devised, some 
of them of proved merit. Others are useless, some of them 
being merely schemes of unscrupulous promoters. The most 
of the methods depend on the constant agitation of the hide 
in the presence of the tanning agent to produce the quickly 
tanned leather so much desired. It is in the preliminary 
treatment of the hides and in the strength and method of 
applying the tanning material that the methods differ. The 
claims as to time required var}^ with each process, some being 
as low as 48 hours from the time the hide leaves the beam 
house until it is said to be ready for the dry loft. 

In one general class of these quick tannages, rockers similar 
to those used in the first stages of some kinds of the regular- 
process sole leather, are employed. In another, revolving 
wheels, or drums, are used for a part or all of the tanning 
process. 

78. In the process involving rockers, the stock that comes 
from the beam house is hung on rockers in the tanning vats. 
The vats are in complete sections and are equipped with the 
press system. The top of one vat is connected with the bottom 
of the next, and the liquor supplied to the head, or strongest- 
liquor, vat gradually works around through all the vats to the 
weakest-liquor vat, from which it flows to waste, or else to 
be strengthened. The stock is hung in the vat receiving the 
weakest liquor, and here it is constantly rocked in contact 
with liquor coming from the next vat. The liquor gradually 
becomes stronger until the vat is receiving the strongest liquor. 
The stock is then removed and may be put into a strong 
lay-away vat for a few days, or it may be wheeled with strong 
liquor or extract, according to the particular quick-tannage 
process that is being used. In some processes, the hides receive 
a chemical treatment before going into the tan liquors. One 
method calls for rocking in a liquor composed of salt, alum. 



MANUFACTURE OF LEATHER, PART 1 43 

and sodium nitrate ; another calls for a light chrome treatment, 
while others call for other baths of single chemicals or com- 
binations of chemicals. Treatment with weak organic acids 
is also generally resorted to, in order to bate and plump the 
stock before going into the tan liquor. All these chemical 
baths are designed to open the pores of the hide, so as to 
facilitate the quick combination of the tanning material with 
the hide, to prevent the drawing, or closing up, of the grain 
when the hide comes in contact with a strong tanning solution, 
and to taw the hide slightly, so that the absorption of vegetable 
tannin by the partly mineral-tanned hide is increased and 
quickened. 

79. Another general class of quick-tanning processes 
requires the use of the revolving drum, or wheel, to effect the 
tanning. Various styles of wheels have been introduced and 
patented, and in many cases the style of wheel or drum used 
is the only protected feature of the process. The wheels are 
generally about 10 feet in diameter and are revolved at varying 
speeds. The interior of the wheels used in some processes are 
fitted with arrangements for fastening the hides by one end 
or edge, so that as the wheel revolves the hides are submerged 
in the tan liquor at one point of the revolution and stretched 
out and drained at another point. Another style of wheel has 
a removable frame shaped like a skeleton wheel, on which the 
hides are fastened in a parallel row, the frame being then 
fastened within the wheel, with which it revolves. 

Another patented wheel contains a removable frame to 
which the hides are attached in a parallel row, but which does 
not revolve with the wheel. The frame is so constructed that 
the hides fastened to it are stretched in alternate directions by 
mechanism actuated by the turning of the wheel. The hide 
frame remaining stationary, the tan liquor is poured over the 
hides by means of buckets or carriers attached to the interior 
of the revolving wheel. The buckets scoop up the liquor at the 
low point of the revolution and dump it at the high point, thus 
allowing it to fall over the hides attached to the stationary 
frame. 

393—-? 



44 MANUFACTURE OF LEATHER, PART 1 

All the wheels are fitted so as to allow the admission or 
removal of the tanning material without interfering with their 
revolution. One process employs a wheel in which the tanning 
material in the shape of solid extract is placed in latticed 
receptacles within the wheel, the weak liquor used in starting 
being strengthened by the slowly dissolving extract. The 
wheels used in processes requiring heat, or the admission of air 
or other gases, are arranged to meet all the requirements of 
the process. 

80. In general, the treatment of the hides in quick-tannage 
processes using wheels is the same as in the processes using 
rockers. Some processes call for a preliminary treatment, and 
others begin with the hide just as received from the beam house. 
Weak liquors are first supplied to the wheels, the strength 
being gradually increased as the tanning progresses, until the 
maximum strength of liquor is being used and the wheel tan- 
ning is completed. The wheels are sometimes run in sets, the 
liquor from a wheel containing hides nearly tanned being run 
to the next wheel in which the tanning is not so far advanced, 
and so on to the wheel containing fresh hides. From here, the 
liquor is run either to waste or to storage to be strengthened. 
Where the wheel is operated as a unit, each sapped liquor may 
be run off to give place to a stronger one, or the liquor may be 
strengthened in the wheel by the addition of strong liquor 
or extract. 

After the wheel treatment, the stock may be bleached and 
lofted, as in some processes, or it may receive a further treat- 
ment by laying away for a few days in a strong liquor, or by 
being thrown loose into revolving, wheels containing strong 
liquor or extract. When the tanning is completed, the leather 
is bleached, oiled, dried, and rolled in the same manner as 
the regular long-tanned leather. 

81. Most of the quick-tannage processes are still in the 
experimental stage, and they find many opponents among 
the old-style tanners. The principal objection to the proc- 
esses themselves is found in the accumulation of weak tan- 
ning liquor. The hides are treated so that their affinity for 



li 



MANUFACTURE OF LEATHER, PART 1 45 

tannin is developed to the highest point, and the strong liquors 
they receive are sapped quickly; thus, a liquor containing a 
preponderance of non-tanning matters ultimately results. 
These sapped liquors may contain considerable tannin, but in 
the presence of such a large proportion of non-tannins, the 
tannin itself is not very active and is not available for quick- 
tanning purposes. The constant strengthening of these liquors 
serves only to postpone the ultimate end of their usefulness and 
to increase proportionately the barkometer strength of the 
waste liquors. 

The principal objection to the manufacture of sole leather 
by quick processes has been its low gain. Unless loaded, or 
weighted with adulterants, the quick-tanned leather produced 
at a cost allowing a profit to the tanner, does not show the 
gain that it is possible to make by the older methods of 
tanning. In the beginning of the quick process, the first 
leather produced may show up well as to gain and as to cost 
of manufacture, but as the process continues it has been the 
experience of many that gain decreases and costs increase. 
The waste of unavailable tannin in the sapped liquors and the 
decreasing purity of the tan liquors are responsible for this 
condition. 

There is also an objection to quick-tanned sole leather 
simply because it is quick tanned, some persons claiming 
that it is impossible by shorter processes, to produce a leather 
with the toughness, mellowness, and fiber of the long- tanned 
methods. This cannot be proved by the characteristics of 
quick-tanned leathers taken as a class, as leather produced 
by quick-tannage methods varies in appearance, texture, and 
strength just as much as the long-tanned leather. 

As previously stated, most of the quick-tanning processes 
are still in the experimental stage, and the exact status of 
quick-tanned leather is not yet determined. From present 
indications, however, it would seem that in the near future 
the practicability and economy of the quick tanning of sole 
leather will be demonstrated. Whether experience will show^ 
it 'to be the equal of the old-style leather remains to be seen. 



MANUFACTURE OF LEATHER 

Serial 416B (PART 2) Edition 3 



HEAVY, OR FIRM, LEATHER— (Continued) 



SOLE-LEATHER MANIIFACTTIRE — (Continued) 



OAK-TANNED BELTING LEATHER 

1. Oak-tanned belting leather is really a sole leather, 
slight changes in the tanning and in the treatment of the 
leather after tanning being made to produce the tough, mellow 
leather that is required for belts. The hides should be the 
best, and the unbranded packer steer hide is used largely for 
this purpose. The beam-house process is about the same as 
for other oak leather, except that the hide is not split into 
sides. The hides are thrown over sticks and hung in the 
handler liquors, instead of being strung together. After 
coming out of the handlers, the bellies are trimmed off, and 
sometimes the heads are taken off at this point. The parts 
trimmed off are strung together and tanned separately, or 
they may be thrown in on top of the regular stock. 

After trimming out the handlers, the hides, or butts, are laid 
on frames in the lay-away vats and care used to spread out 
smoothly and remove all creases. The frames are held by 
ropes attached to the comers and are gradually lowered into 
the vat as the height of the hides on the frame increases. 
This stock is generally given five or six layers, the first, and 
sometimes the second, being sour liquors that have been sapped 
by higher layers. 

COPYRIGHTED BY INTERNATIONAU TEXTBOOK COMPANY. ALU RIGHTS RESER\ED 



MANUFACTURE OF LEATHER, PART 2 



2, The schedule for a typical belting butt yard is given in 
Table I. 

The leather is hoisted twice while in the first lay-away 
liquor, the hides being removed and carefully piled beside the 
vat. The creases and folds are removed and the hides flattened 
out in the piling, and the leather is again laid away in the 
same liquor. This treatment seems to improve the quality of 
the butts, and while it is not followed in all tanneries, the 
appearance of the finished product that has undergone this 
treatment in the yard would indicate that it is worth while. 
If the leather out of the first layer is flat and free from creases, 

TABLE I 

LAYER SCHEDULE FOR OAK-TANNED BELTING LEATHER 



Layer 


Character 


Strength 
Degrees Barkometer* 


Time 
in Days 


First 


Sour 
Sweet 
Sweet 
Sweet 
Sweet 


37 
30 
33 

38 

50 


15 


Second 

Third 


10 
15 


Fourth 

Fifth 


30 
50 







there is small probabiHty that the higher layers will cause a 
permanent crease or wrinkle, as the first layer tends to firm up 
the soft stock from the handlers. 

After being raised from the last layer, the stock is put into 
cold water overnight, and then into water ranging from 90° to 
100° F. for the same length of time. It is then taken out 
of the warm water, carefully piled, and allowed to drain. 
When drained, it receives a hand oiling with cod oil on 
the fiesh side and it is again piled to allow the oil to. work 
into the leather. The leather is then lightly oiled on the 
grain side, taken to the dry loft, and, when dry, is ready for 
shipment. 



*See Art. 23. 



MANUFACTURE OF LEATHER, PART 2 3 

3. Harness Leather. — Green, salted, heavy cow and steer 
hides that go through the regular liming process in the beam 
house are used for harness leather. The hides are bated with 
oropon, or with an organic-acid solution. Rockers are used to 
rock the sides in the first weak tanning liquors. After the 
rocker treatment they receive three or four lay-away liquors, 
oak bark being used between the layers of leather in the vats. 
The best harness leather is pure oak-bark tanned, but much of 
the present product is tanned with liquors made up of chestnut- 
wood and quebracho extract in combination, with oak- and 
hemlock-bark liquors. The flesh is given a smooth stirface by 
skiving, or shaving, when the leather is pretty well struck 
through. 

4. After tanning the leather is scoured. It then receives 
a light coat of cod oil on the grain side and is hung up to 
sammie, or season. When properly seasoned, the sides are 
thrown on the setting table, the flesh smeared with tallow 
and oil, and the grain side thoroughly worked with a stone. 
It is then given another coat of cod oil. The flesh side is then 
worked, additional oil and tallow are put on, and the side 
suspended to dry slowly. When nearly dry, the grain side is 
again worked, or set, and oiled, and the side is again hung up 
to dry. From the loft the leather is piled and remains in the 
piles for 10 days or more, when it is buffed and blacked. The 
buffing is generally done by hand, a light shaving of the grain 
being removed to obtain a uniformly smooth surface. After 
buffing a hot solution of sal soda and logwood is applied with 
a stiff -bristled brush, and thoroughly rubbed in. This saponifies 
the surface grease and oil, so that it will not interfere with the 
coloring. It also mellows the grain of the leather. The black- 
ing is then applied with a soft brush, or swab, and then allowed 
to dry partly. After this another application of a thin mixture 
of oil and tallow or stearin is given the leather, which is rehung 
on sticks. After a hand setting-out on the following day, a 
final coating of oil and tallow is applied and the leather is again 
hung up to dry. After drying the sides are removed from the 
racks and arranged in piles where they remain from 1 to 2 



4 MANUFACTURE OF LEATHER, PART 2 

weeks. The leather from the piles is finished by slicking off 
the grease from the flesh side and smoothing it. The grain 
side is then slicked and brushed and finally rubbed with a 
woolen cloth. The leather is then trimmed and graded for 
market. 

VEGETABLE TANNING MATERIALS 

5. As a result of the diligent research that has been going 
on for many years the number of available vegetable tannins 
has been greatly increased and as a result the cost of tanning 
materials has been lessened. 

Of late years the economical leaching of the bark has served 
to lengthen the time during which the native barks will be 
available. The use of wood extracts has also served to protect 
and increase the life of bark tanning, and as the supply of wood 
from which these extracts are made is practically unlimited, 
this generation at least has nothing to fear from a shortage of 
tannins. 

6. In tanning hides for sole leather, the following vegetable 
tanning materials are most frequently used: 

Hemlock hark is the most important vegetable tanning 
material used in America, about 60 per cent, of all leather 
being tanned by it. It is the bark oiAhies Canadensis, and in 
the East it contains about 11 per cent, of tannin. The tannin 
content of Western hemlock runs as high as 18 per cent. Hides 
tanned with it make tougher leather than those tanned with 
oak bark, but the leather is not as pliable. Both solid and 
liquid extracts of hemlock bark are also on the market. 

Oak hark is also one of the important tanning materials. 
It is the inner bark of several varieties of the oak tree, as the 
English oak {Quercus rohur), the rock-chestnut oak (Quercus 
monticold), and the yellow oak (Quercus tinctoria). White oak 
{Quercus alba) and the red oak (Quercus rubra) are not so val- 
uable because of their lower tannin content and undesirable 
color. The tannin of the several varieties of oak is known as 
quercitannic acid, CuHgOq. There are four anhydrides of this 
acid, the first, phlobaphene, C^iHsoOii', the second, C34^28 0i6; 



MANUFACTURE OF LEATHER, PART 2 5 

the third, Oser's oak red, C^JImOu\ and the foiirth, Lowe's oak 
red, Cs^2iOu. Quercitannic acid and phlobaphene only are of 
importance in tanning. 

Canaigre {Rumex hymenosepalus) is a native of the dry 
Southwest. Some recent attempts have been made to cultivate 
it and introduce it as a tanning material, but with little success. 
The coloring matters and starch extracted from it affect the 
quality of the leather. 

Quebracho is the name of several hardwood trees growing in 
South America. The wood and bark of Quebracho Colorado 
contain from 15 to 20 per cent, of a bright-red tannin, but do 
not contain enough non-tannins to aid the formation of fer- 
mentative acids necessary to plumping, nor will it yield a full, 
well-nourished leather unless combined with other forms of 
tanning agents that are richer in non-tannins. 

Palmetto root is obtained from the palmetto tree found 
abundantly in the Southern lowlands. This root has been 
attracting considerable attention for the past few years among 
Southern tanneries. The root is cut up and treated like bark. 
Its action is quick, and the leather tanned by it is tough. 

Gambier {pale catechu) is an important tanning agent. It is 
the dried extract from the leaves of Uncaria gambier and 
Uncaria acida. The extract is readily soluble in warm water. 
It contains from 36 to 40 per cent, of a brown tannin that 
penetrates hides rapidly and tends to swell them; taken alone, 
it produces a soft, porous tannage. It is largely used with 
other tanning materials for both light and heavy leathers. 
It is exported from Singapore in pressed blocks and cubes. 

Catechu, or cutch, is the dried extract of an East Indian tree, 
Acacia catechu. It contains from 45 to 55 per cent, of a special 
variety of tannic acid. The extract is evaporated until a 
thick, dark-brown product is obtained, which solidifies on 
cooling, and is exported in this form. 

Gallnuts, or nut galls, are excrescences on certain plants, 
caused by gall flies, which puncture the bark in order to deposit 
their eggs. Oak gall, or Aleppo galls, and Chinese galls are 
the most important. The oak gall is formed by the insect on 
Quercus infectoria. The eggs hatch and the larva develops 



6 MANUFACTURE OF LEATHER, PART 2 

within the gall. The best galls are gathered before the fly 
becomes fully developed, and contain from 60 to 70 per cent, 
of gallotannic acid. The Aleppo galls are the most valuable. 

Mangrove bark has of late years become popular as a cheap 
tanning agent. The mangrove tree grows in swamps in 
tropical and semitropical countries, and the bark contains a 
quantity of tannic acid, varying with the locality of grov/th. 
The African bark is the strongest in tannin, running as high as 
45 per cent.; South- and Central-American bark contains as 
much as 28 per cent., while the Florida bark rarely has more 
than 22 per cent, of tannin. When used alone, the African 
bark gives a rather harsh leather of a bright-red color, but it 
makes an admirable combination with native American barks. 

Sumac in all its varieties is a common and valuable tanning 
agent. It consists of the powdered leaves of the so-called 
tanners' sumac {Rhus coriana, R. typhina, etc.). The best 
sumac comes from Sicily, but Italian, Spanish, French, and 
American sumac is also found on the market. Sumac contains 
from 15 to 30 per cent, of a light-colored tannin, which is in 
great demand in the manufacture of some classes of leather. 

Chestnut wood is largely used for extract manufacture in the 
United States, but, mixed with bark, its use in the tannery 
leach house is becoming quite common. The wood found in 
the Northern states contains from 5 to 8 per cent, of tannin, 
while Southern chestnut wood often contains as high as 11 per 
cent, of tannin. The chestnut tree, being of quick growth, 
offers a solution to the problem of offsetting the decrease in 
vegetable tanning agents. The chestnut blight, however, which 
has devastated the Atlantic Coast, places this industry in a 
very serious position, and every effort is being made to check 
the disease. 

Valonia is the commercial name for the acorn cups of several 
species of oak (Quercus cegilops and Quercus macrolepis) coming 
from Asia Minor and Greece. They contain from 25 to 35 
per cent, of tannin, • somewhat resembling that of oak bark, 
but giving a browner color and heavier bloom. It makes a 
hard, water-resisting leather and is sometimes mixed with oak 
bark for use in sole-leather tanning. 



MANUFACTURE OF LEATHER, PART 2 7 

Divi divi is the dried seed pods of a South American bush. 
The pods are about 3 inches long, of a brownish color, and in 
drying bend in the form of the letter S. These pods contain 
from 30 to 50 per cent, of a peculiar tannin somewhat similar 
to that of valonia. 

Myrohalans are the dried fruit of several species of Terminalia 
from Hindustan,, Ceylon, and other countries. They contain 
from 28 to 35 per cent, of tannin, and are generally used in 
combination with other tanning agents. Some varieties cause 
a bloom similar to that of oak bark, and all varieties are great 
acid formers in the tan yard. 

Mallet hark is an Australian product containing as high as 
50 per cent, of tannin similar in color to oak bark. 

7. Classification of Taimins. — The tannins in tanning 
materials are different members of a large group of organic 
bodies known chemically as tannic acids, or tannins. They 
differ widely in chemical constitution and reaction, but all 
have the common property of precipitating gelatine and 
forming soluble compounds with animal tissue. They are 
all compounds of carbon, hydrogen, and oxygen, but their 
ultimate structure is little understood. 

When heated, the natural tannins yield catechol, CqH^{0H)2, 
or pyrogallol, C&Hz{0H)2., and sometimes both. The classifi- 
cation of tannins on these chemical lines bears out an old classi- 
fication made on the appearance of the tannage. 

8. Tannins were formerly divided into those which yield the 
whitish deposit on the surface of the leather, called bloom, and 
those which do not. Most tannins that give a bloom to the 
leather are pyrogallol tannins; a solution of their non-tannins 
when separated has an opalescent appearance. The tannins 
that give no bloom to leather are classed as catechol tannins. 

When treated with sulphuric acid, the pyrogallol tannins 
yield gallic acid or ellagic acid, the latter combining with tannic 
acid to form the bloom. Under this treatment, the catechol 
tannins yield the reddish-brown insoluble bodies known to all 
tanners as reds. These reddish-brown insoluble bodies differ 
from the original tannins in containing fewer molecules of 



8 MANUFACTURE OF LEATHER, PART 2 

water, and are, therefore, anhydrides of their especial tannic 
acids. 

Hemlock bark yields a series of these reds; the higher mem- 
bers are soluble, precipitate gelatine, and are the principal 
coloring materials of the bark. The lower members are 
insoluble at ordinary temperatures and form the sediments 
found in the tannery vats. 

9. Wood and Bark Extracts. — The use of wood and bark 
extracts in the process of tanning is becoming more general 
every year. There are few tanneries where extract is the exclu- 
sive tanning agent, and but few tanneries where it is not used 
to some extent. Primarily, an extract is valuable because of 
the annual decrease of tan bark that its use has brought about. 
It brings the strength of distant virgin forests to the aid of 
our own failing supply of bark. It is decidedly useful as a 
convenient means of strengthening a weak liquor quickly, 
without the addition of the same amount of insolubles that 
would be added were the ordinary bark liquor used. The 
extracts made from some barks and woods are valuable for 
the color that they impart to inferior tannages on which they 
may be used. 

In sole-leather manufacture, extracts are generally used for 
strengthening the liquors and occasionally for improving the 
color of the stock. In some branches of the upper-leather 
industry, the pelts are partly tanned in bark liquors and then 
finished in liquors made up entirely of extracts. In this way 
the distinctive characteristics of the tannin of the bark or wood 
from which the extract was made, are imparted to the skins. 

In the shortened method of modem sole-leather tanning, 
the undiluted liquid extract is drummed into the tanned hides, 
thereby saving time and increasing the weight of the leather. 

10. Manufacture of Extracts. — The manufacture of 
extracts is carried on to a large extent in the United States, 
South America, Europe, and Asia. Wherever there is a 
sufficient supply of tanning material, handicapped by prohibi- 
tive freight rates, the extract works solve the commercial 
problem of economical distribution. 



MANUFACTURE OF LEATHER, PART 2 9 

The material to be extracted is ground fine and the leaching 
takes place in the same manner as at the tannery ; details as to 
the duration of the leaching, temperatures, etc., are determined 
by the particular substance undergoing extraction. To remove 
fine, insoluble materials, the liquor is then treated by some sort 
of clarification process, either mechanical or chemical, or both. 

Numerous methods of clarification are in use among extract 
manufacturers. Dried blood and other albuminous products 
are used and in coagulating, envelop the solid particles and 
settle out. Inorganic processes, such as the use of acetate of 
lead, or the direct precipitation of barium sulphate in the tank, 
have been devised, but these processes remove more or less 
tannin, in addition to the insolubles taken out. Purely 
mechanical processes of clarification consist in the settling of the 
liquor in vast settling tanks or by slow filtration through some 
coarse fabric. 

The older methods of clarification depended on the removal 
of the insoluble particles, or reds, to accomplish the clearing 
of the liquors. The later clarifying processes aim to make 
these reds soluble, thus making a clear extract, and at the 
same time rendering the reds available as tannins. For this 
purpose, sulphurous acid, alkalies, or bisulphite of soda are 
used. When these chemicals are used, the clarification of the 
extract should not take place until the concentration of the 
liquor has been nearly accomplished. The use of alum or 
salts of aluminum and chromiimi, is also frequently resorted to, 
in order to remove from some extracts the objectionable red 
color like that made from hemlock bark, and also from some 
varieties of quebracho wood. 

11, The liquors from the leach house are concentrated in 
vacuum apparatus, multiple-effect vacuum pans generally being 
used because of the resulting economy in the cost of opera- 
tion. A standard quadruple-effect pan is shown in Fig. 1. 
Each efect is exactly like the others and consists of a cylindrical 
copper body a bolted to a steam dmm h. The steam drum in a 
standard vacuimi pan consists of a circular drum of copper 
having a great number of vertical copper tubes, the upper and 



MANUFACTURE OF LEATHER, PART 2 11 

lower ends of which are expanded into openings in the upper 
and lower heads of the drum. The steam drum has a circular 
well in the center, generally of a diameter equal to one-third 
the diameter of the drum. The piirpose of the well is to help 
the circulation of the liquors while they are boiHng. Vapor 
pipes lead from the top of th-e body of one effect to the steam 
drum of the next, the vapor pipe from the last effect being con- 
nected with the condenser. Pipes for conveying the thin liquor 
to each pan, and for conveying the liquor from one pan to the 
other, are provided. Pipes for conducting the condensed steam 
and vapors from the steam drums and for removing the finished 
extract from the last effect are also provided. 

Liquor is put in the pan, condensation water removed from 
the steam drums, the finished extract removed from the last 
effect, and the vacuimi maintained by different pumps adapted 
to the work. 

12, In operation, the pans are charged with liquor, pumps 
are started, and steam turned into the steam drum b of the 
first effect; the steam surrounding the multitude of tubes in 
the steam drum is rapidly condensed, and the liquor in the pan 
soon begins to boil. The vapor from the boiling Hquor passes 
through the vapor pipe c into the steam drum b of the second 
effect, gives up its heat to the liquor in this effect, and is con- 
densed. The vapor from the liquor in the second effect goes 
through the vapor pipe d to the steam drum b of the third effect, 
and the vapor from this effect goes through the vapor pipe e to 
the steam drum b of the fotirth effect. The vapor from thf 
fourth effect goes through the pipe / to the condenser, where i.; 
is condensed by a spray of cold water. The condenser is 
attached to a leg pipe about 35 feet long, having its lower end 
sealed in a water well overflowing to the sewer ; the suction 
pipe of a vacuum ptimp is attached to the lower part of the 
condenser and maintains a vacutim of from 24 to 27 inches of 
mercury in the condenser and last effect. This lowers the boil 
ing point to such an extent that liquor boils in the last effect at 
a temperature close to 150° F. Vapor coming from the thii'd 
effect is quickly condensed in the drum of the foiirth effect 



12 MANUFACTURE OF LEATHER, PART 2 

and causes_a decrease in pressure in the body of the third effect. 
The boiHng point in the third effect is thus lowered, causing a 
slight vacuum that influences the pressiu-e and boiling point in 
the second effect, and in turn the condensation of vapors com- 
ing into its steam drum is thereby quickened. 

The vacuiun on the first, second; and third effects is materially 
increased by the suction of the pump used to remove the con- 
densation from the drums. In practice, it is customary to 
maintain a steam pressure of 5 pounds on the drum of the 
first effect, a very slight vacuum in the first effect, and a regular 
increase in vacuum thereafter, until the maximum is reached 
in the last effect. The liquor is pumped into the first effect, 
from which it is sucked to the second, and from the second to 
the third, and from the third to the fourth, the liquor in all 
effects being maintained at the desired level by regulating the 
valves on the pipes connecting the pans, so that enough is 
admitted to replace the amount evaporated. When the 
desired concentration is reached, the extract is slowly pumped 
from the last effect to the clarifying tank, or to the storage tank 
in case the liquor is not to be clarified. 

13. Some extracts are marketed with a specific gravity of 
1.22, or 44° Twaddell, others are still further reduced to a 
specific gravity of 1.26, or 52° Twaddell, while practically all 
the foreign extracts come to the United States in the solid 
form, containing from 20 to 25 per cent, water. For evaporat- 
ing to dryness the strike pan or drum dryer is used. 

Hemlock-bark extract has been longest on the market. It is 
made from the common hemlock bark in localities where hemlock 
grows plentifully and is shipped to other less-favored points. 

Rock-oak bark, chestnut-oak bark and wood, mangrove, sumac, 
quercitron, mimosa, quebracho, gambier, acacia, and other woods 
and barks are extracted, and their extracts form valuable 
adjuncts to the ordinary tan liquor. 

Among American tanners, the standard extracts are que- 
bracho and chestnut wood. 

Quebracho extract is made from the wood of the quebracho 
tree, a close-fibered South American wood. It produces a 



MANUFACTURE OF LEATHER, PART 2 13 

fine-colored tannage, but is better adapted to the tanning of 
upper leather than for sole leather, as its low non-tannin 
content tends to keep it sweet; that is, it does not foster the 
growth of organic acids necessary to pliunping. 

Chestnut-wood extract is made from the wood and bark of 
the chestnut tree, found in nearly all parts of the United 
States. Used in connection with other tanning materials, it 
is perhaps the most valuable of extracts. The tree grows 
quickly, and if the young trees on a stripped tract are forested, 
the original growth will be duplicated and large enough to cut 
in 15 or 20 years. 

14, Preparation and Leaching of Bark. — The leaching 
of bark is an operation in tanning which has caused the loss of 
thousands of dollars through improper manipulation. Even 
at this late day, tanners are leaving in the cast-off bark as high 
as 25 per cent, of its original tannin content. When the theory 
of leaching is thoroughly understood, there will be no such 
wanton waste. 

The principles of saturation and equalization underlie the 
theory of leaching. A piece of hot iron placed in water loses its 
heat to the water and becomes colder, while the water is 
warmed by the iron and finally both iron and water are of the 
same temperature. The same principle is involved in the 
process of leaching; both the leach and liquor ultimately 
become of equal strength. A strong liquor run on a spent 
leach will come off the leach weaker than when it ran on. 
In a perfect leaching system, the object is always to run a 
liquor on a leach that can add tannin to the liquor. 

15. Preparation of Bark for Leaching. — Various 
methods of preparing the bark for leaching are in use. They 
all consist of some kind of grinding and shredding. Proper 
preparation of the bark is important and quite essential to 
close leaching; the best leaching system will not produce good 
results unless the bark is reduced to such a state that the 
water or liquor can readily penetrate to every fiber. 

Mills for grinding bark have the common feature of a revolv- 
ing disk into which cutting knives are set radially. Most of 

393—5 



14 MANUFACTURE OF LEATHER, PART 2 

them have a secondary disk that completes the work which 
the first disk started; the bark then passes through small 
apertures to a conveyer. 

16. Ott Bark Mill. — The Ott mill, shown in Fig. 2, is 
the most popular of the grinders. It consists of a hopper a, 



Fig, 2 



leading to the lower part of the mill, where the grinding is 
done. A shaft b, by means of which the mill is driven, runs 



MANUFACTURE OF LEATHER, PART 2 



15 



through the center of the entire mill, which may be driven by 
it from either the top or the bottom. The portion of the 
shaft running through the hopper has keyed to it four pro- 
jecting iron arms c, which, with the aid of similar projections ci 
from the inner sides of the hopper, break the bark into small 
pieces that fall into the runner, or carrier, shown in Fig. 3 (a) . 
The runner, or carrier, consists of a circular piece of steel d 
fitting the lower part of the mill; it is attached to and revolves 
with the shaft that passes through its center. Attached to 
the shaft above this disk are four angular iron wings e that 





Fig. 3 

extend to the edges of the disk and are attached to it by bolts 
engaging the flanges of the wings. The ends of the wings are 
supplied with steel tips e' that form a cutting surface. The 
knives /, Fig. 2, are set vertically and bolted to a slotted 
cylinder of the same height as the runner, and surrounding it. 
The bark, having been broken by the upper arms, falls into the 
runner and is ground by being carried against the knives by the 
steel-tipped wings. Passing through the knife slots, the bark 
falls into the bottom of the grinder and is delivered by means 
of a spout g to the carrier k, which takes it to the leach house. 



16 MANUFACTURE OF LEATHER, PART 2 



The cylinder, shown in Fig. 3 (6) , containing the knives /, 
is made in segments that can be removed for the grinding and 
setting of the knives, five of which are held in each segment. 
The mill is run at a speed of 100 to 150 revolutions per minute; 
the knives require grinding and setting at intervals which 
depend on the character of the material that is ground. 

Many tanners prefer a shaving machine that reduces the 
bark to shreds instead of grinding it. With oak bark it gives 
better results than the ordinary grinder. 

17. Williams Patent Bark Sliredder. — The machine 
shown in Fig. 4 is the best known form of the shaving, or 

t. 




Fig. 4 

shredding, type of machine. It is cylindrical in shape, the 
casing a surrounding a horizontal shaft to which a hub h is 
keyed. Heavy, sharp-pointed arms, or hammers, .c that pre- 
sent a cutting edge, are hinged to the hub by pinions, and 
when the shaft is in motion the centrifugal force causes them 
to radiate from the hub. The hopper d is at the side, the 
floor of the hopper being inclined by a raised plate, the end of 
which forms a sharp breaking comer so that the bark is cut in 
small pieces before the final shredding takes place. A segment 
of a cylinder, shown at the left in Fig. 4, contains the knives e 



MANUFACTURE OF LEATHER, PART 2 17 

and is so placed beneath the revolving arms that the edges of 
the knives and the sharp ends of the revolving arms form shears 
and cut or shred the bark forced between them. The shredded 
bark then falls between the knives into the conveyers. The 
segment, or cage, containing the knives is in the form of a 
semicircle, and the knives are so arranged that the lip, or 
projecting edge, presents a shaving, or shredding, siirface 
rather than a pulverizing surface. The knives can be taken 
from the cage, resharpened, and replaced. A bowed steel 
shell /, with one edge riveted to the top of the casing and the 
other edge projecting through the hopper opening into the 
cylinder, forms a chamber for the settling of the dust after it 
has been moistened by a spray of steam introduced at the side 
of the hopper at g. Economy of power with greater grinding 
capacity is claimed for this type of machine; it is especially 
valuable for wood and barks of a fibrous nature. 

When ground, the bark is conveyed to the leach house by 
a mechanical conveyer or blower, the former being the cheaper 
method of conveyance. 

18. Yat Leaching. — Most of the older leach houses were 
constructed by sinking the vats in the ground. While this 
method seems to economize the heat used in latter-day leaching, 
inability to repair leaks is a serious objection to this form of 
construction, and all the newer types of leach houses are con- 
structed with the bottoms of the vats above ground. In this 
way, leakage is detected and stopped, and the spent, or 
exhausted, tan is much more easily removed from the lea;ching 
vats. Mechanical contrivances for handling the bark before 
and after leaching are in general use. The vats, or leaches, 
are filled from an overhead conveyer leading from the bark 
storehouse; and when the bark has been leached, the spent 
tan falls through an opening in the bottom of the vat into a 
conveyer that takes it to the furnace, where it is used as fuel. 

The vats used for leaching are usually arranged and worked 
in sets; the vat containing the freshest bark is known as the 
head-leach and that containing the nearly spent bark is called 
the tail-leach. 



18 MANUFACTURE OF LEATHER, PART 2 

The vats, or leaches, arranged in sets or sections are provided 
with perforated false bottoms, and they are so piped that the 
liquor from the bottom of one leach is delivered to a box on the 
top of the next leach in the section and falls either directly on 
the bark or is distributed over its surface by means of an 
arrangement known as the sprinkler. The sprinkler is made of 
two pieces of brass pipe screwed into a tee, which, by means 
of a swivel joint, is connected with the pipe leading down 
from the box on top of the leach. Each arm of the sprinkler 
has a row of perforations, and the ends of the arms are closed 
by removable caps to allow cleaning. The perforations on one 
arm are opposite those on the other, so that when liquor flows 
through the box into the sprinkler one arm delivers liquor in 
one direction, and the other arm delivers it in the opposite 
direction. This causes the sprinkler to revolve and spread the 
liquor over all parts of the bark. 

19. The general scheme for leaching with vats is to run 
water on the tail-leach, and after the liquor comes off it is put 
on the next, and so on throughout the set until the liquor 
comes off the head-leach, when it is sent to the settling tanks 
or storehouse. The tail-leach, after receiving all the water 
intended for it, is emptied or pitched, filled with fresh bark, 
and becomes the head-leach, the leach next above it becoming 
in turn the tail-leach. 

This method of handling the liquors is common to all systems 
of vat leaching. It is in the method of applying the water, of 
removing the liquor from leach to leach, the temperature of 
the liquors, the depth of the vats, and in many other minor 
details that the various systems differ. 

With some systems, the use of warm liquors on every leach 
is advocated, the water going on the tail-leach being as near 
the boiling point as possible; the water becomes cooler as it 
goes to the next leach and finally becomes too cool, in the 
judgment of the advocates of this system, and is reheated. 

Some leaches have steam coils, protected from the bark by 
a false bottom, in order to maintain the temperature deemed 
necessary for proper leaching. Other leaches have in the box 



MANUFACTURE OF LEATHER, PART 2 19 

on the top of the leach a coil of steam pipe for heating the 
liquor from the preceding leach. Hot leaching, if not carried 
to extremes, is the most economical method. When the con- 
tinued use of very hot waters is resorted to, the reds and the 
resinous matters of the bark are dissolved in the liquor. These 
reds are of no use in tanning operations, and serve to make an 
impure liquor, because their proportion to the amount of tannin 
that is removed by the extra heat is altogether too large to be 
economical. 

Within certain limits, the higher a column of bark through 
which a liquor passes, the stronger is the liquor and the more 
perfect the leaching; the weight of the column is limited by 
its interference with the circulation of the liquor. When the 
leach is too deep, the bark packs down tightly and stops the 
even percolation of the liquor. 

20. In some systems of leaching, the liquors are moved 
from leach to leach by pirnips worked by a common rod. The 
conditions, however, are not the same in each leach, and hence 
ptimping devices should be fitted to each leach separately, so 
that the regulation of their speed may be under control. 

The air system of handling leach-house liquors is now quite 
common, and it is probably the best method of moving these 
liquors. Compressed air is admitted to the bottom of the 
upright pipe that conveys the liquor from the bottom of one leach 
to the top of the next, and raises the colimm of Hquor in the pipe 
until it flows into the liquor box on the top of the next leach. 

The practice in some tanneries is to empty a leach of liquor 
entirely and then run on more liquor. The leaches should be 
kept covered with liquor at all times. If one is drained free 
from liquor, the bark settles down and packs tightly; the 
liquor running on the bark in this state channels its way to the 
bottom and uniform percolation is not secured. 

A constant and slow influx of liquor on the leach is preferable 
to a large stream. The liquor should be given a long contact 
with the bark. It should be delivered on the top of the leach 
in a divided stream and not in a single strong jet. Liquors 
that are partly spent are frequently returned to the leach 



20 MANUFACTURE OF LEATHER, PART 2 

house in order to be strengthened and to keep up the general 
strength of the leach-house liquors. The returned liquors are 
generally run on the upper leaches of the section, as the lower 
leaches, being nearly spent, would take strength from, instead 
of adding strength to, the liquor. While the partly spent 
liquors have lost a considerable share of their tannin during 
the tanning operations, they still retain a large proportion of 
their original non-tannin content; when strengthened, therefore, 
they do not represent the tannin strength that is possessed by 
a new liquor of the same specific gravity. 

21, A complete description of a leaching system will give 
a general idea of the mode of operating. The leaches are 
circular in form, 12 feet in diameter, and 15 feet deep, with 
plank covers, and with heater boxes on top of them. The 
liquors are moved by means of the air system. Water as near 
a temperature of 212° F. as possible is run on the tail-leach, 
from the bottom of which it is pumped to the heater box of 
the next leach. Here it is reheated while passing over the 
steam coils and falls through a pipe into the leach. The liquor 
passes through each leach successively and is reheated until it 
reaches the leach next to the head-leach. Here, it is not 
reheated, but passes through the bark and comes into the box 
on the head-leach at about 150° F. The sprinkler used on the 
head-leach distributes the liquor over the surface of the bark. 
When the head-leach is wet down or filled with liquor, the 
liquor is run off to the cooler or storage vats. The pumping 
from this head-leach is continued until the liquor becomes too 
weak for use in the tannery. When used yard liquors are 
returned to the leach house, they are pumped into the heater 
box on the top of the head-leach, heated, and distributed over 
the bark by the sprinkler. After ail the returned liquor has 
gone into the heater box, the liquor from the leach next to the 
head is pumped into the head-leach and the regular leach-house 
process continues. 

The bark in the leaches is kept covered with water or liquor 
at all times, and the pumping from one leach to the next is 
regulated with this end in view. 



MANUFACTURE OF LEATHER, PART 2 21 

The preceding remarks on leaching apply particularly to the 
leaching of such common barks as hemlock and oak, but with 
other materials the general principles are the same, and, except 
for variations in the size of leaches and in the temperature of 
operation, the method of procediu^e is similar. 

22. For some materials rich in tannin, autoclaves, or 
metallic cylinders, in which the leaching is carried on at different 
pressures, are used. Drum-leaching systems have been used 
on oak and hemlock barks, but for these materials they are not 
necessary; drum systems have been very successfuly used in 
the leaching of some high-priced imported barks and woods 
containing high percentages of tannin. 

23. Density, or Specific Gravity, of Tan Liquors. 

The density of tan liquors is determined by means of a form of 
hydrometer called a barkometer and having a graduated scale 
showing degrees barkometer, or, as it is generally written, degrees 
* *Bk. ' ' One degree Bk. represents the density of a liquor having 
a specific gravity of 1.001, barkometer degrees being the deci- 
mal portion of the specific gravity figure read in thousandths ; 
thus, 10° Bk. is specific gravity 1.010, 45° Bk. is specific gravity 
1.045, etc. 

A barkometer merely shows the density of a liquor, or its 
weight compared to that of water; it cannot determine the 
tannin strength of a liquor, as one 20° Bk. tan liquor might 
contain 3 per cent, of tannin and another liquor of the same 
density might contain only 1.5 per cent, of tannin. Non- 
tannins and other soluble constituents of tan liquors influence 
the density, and hence the mistake should not be made of 
considering a 25° Bk. liquor necessarily stronger in tannin 
than a 20° Bk. liquor. The barkometer readings should be 
made with the liquor at a temperature of 60° F., or else a correc- 
tion should be made to compensate for the expansion or con- 
traction of the liquor. If warmer than 60°, the liquor will 
show less barkometer strength; if colder, it will show more, so 
that all readings should be made at, or corrected to, 60° F. 

The specific gravity of an extract is generally denoted in 
degrees Twaddell. One degree Twaddell is equivalent to a 



22 MANUFACTURE OF LEATHER, PART 2 

specific gravity of 1.005, being one-fifth of the decimal portion 
of the specific-gravity figure when the latter is represented in 
thousandths. Thus, specific gravity 1.225 is 45° Twaddell, 
specific gravity 1.400 is 80° Twaddell, etc. From this relation, 
it is evident that 5° Bk. is equal to 1° Twaddell, or 45° Twaddell 
is225°Bk. 

ANALYSIS OF TANNING MATERIALS 

24, The methods of analysis for tanning materials have 
been gradually developed and are peculiar to this class of work. 
In addition to the general laboratory equipment of apparatus 
and chemicals, there are needed special contrivances and prep- 
arations, such as extraction apparatus, devices for shaking, 
animal charcoal, and a supply of hide powder. 



ANALYSIS OF BARK, WOOD, ETC. 

25. Preparation and Extraction of Sample. — The 

sample is ground so that it will pass through a sieve having 
20 meshes to the linear inch. It is well mixed, and a 10-gram 
sample is dried overnight in a steam oven for moisture deter- 
mination. A weighed portion of the bark is then extracted 
in some form of extractor suited to the nature of the material 
under examination. In all cases, the extractor should be of 
such form as to permit the removal of the first, or strong, 
portions of the extractives, so that these will not be subjected 
to the influence of sustained high temperatures. For materials 
like oak and hemlock bark or chestnut wood, a different 
method of extraction from that required for sumac, algorahilla, 
etc., may be used. 

26. Tlie Reed Extractor. — An extracting apparatus 
suited for use on all materials is that known as the Reed 
extractor, w^hich is shown in Fig. 5. By varying the method of 
operation, practically all tanning materials may be extracted 
by it. For use on sumac or like materials, which do not allow 
of an initial extracting temperature of boiling water, the 
material is weighed into a cup h that has a perforated brass 



MANUFACTURE OF LEATHER, PART 2 23 

bottom and rests on a perforated plate d of the outer vessel a. 
Water is placed in the vessel a surrounding the cup b and is 
kept at the desired temperature by heat applied to the bottom 
of a. Suspended over cup b is an inverted vessel c filled with 
water and having an outlet ^ at a higher level than that of tube/. 




Fig. 5 

Cocks g and h are closed and cock i is opened, and water is 
allowed to flow into the cup. When the desired temperature 
is attained, cock / is partly opened and percolation begins, the 
extractives being delivered through cock / at any desired speed, 
additional water flowing from c as the level falls below the 
opening e. When the strong extractives have been removed, 



24 MANUFACTURE OF LEATHER, PART 2 

cock / is closed and some of the water surrounding b is drawn 
off through cock k until about 600 cubic centimeters of water 
remains in the bottom of a. The inverted vessel c is removed 
and to the flanges at I is attached a conical cap to the apex of 
which a condenser tube is brazed. An annular ring fitted to 
the interior surface of the cap serves to guide the water of 
condensation, so that it falls into the cup b. 

The water in a is then boiled and the condensed steam 
falling into the cup b completes the extraction. The extrac- 
tives may be delivered directly by closing cock g and opening 
either h or /. If continuous operation is desired, cocks h 
and / are closed and cock g is opened, and the extractive is 
returned to the lower part of a. 

27. The Teas Percolator Extractor. — The Teas perco- 
lator extractor, shown in Fig. 6, may be used on all new 
materials, but a large volume of weak extractive solution 
results if used on spent or leached materials. It consists of 
small cylinders surrounded by a heating jacket a, the latter 
being supplied with water from a reservoir through b. The 
reservoir is located above the apparatus so that, when desired, 
the boiling point of the water may be raised above the normal 
boiling point. In operation, the perforated disks on the ends 
of brass rods e are covered with a thin layer of cotton or filter 
paper and the weighed material is brushed or washed into the 
cylinder and covered with water. Heat is applied to the 
bottom of the jacket, and when the desired temperature is 
attained, the cocks c are opened and hot water allowed to drip 
on the material. The extracted material is delivered through 
any of the 'cocks d, depending on whether a flooding or a time 
percolation is desired. After the first portions of the extrac- 
tives are removed, the heat is raised to the boiling point and the 
extraction completed. 

28. Tlie Teas Cumulative Extractor. — ^For all spent 
materials, as well as new materials, like oak and hemlock bark, 
etc., the Teas cumulative extractor, shown in Fig. 7, is more 
convenient than the percolative extractor described in the pre- 
ceding article. The cimiulative extractor may also be used on 



MANUFACTURE OF LEATHER, PART 2 



25 



stunac and similar materials by varying the method of opera- 
tion. In using this extractor, the stem e is connected to a cop- 
per or glass flask and the cap J to a condenser. The cock / 
and side openings k and / are closed. The material is weighed 
or washed in after covering the perforated plate at the bottom 
with a thin layer of cotton or filter paper, and then thoroughly 
moistened. A liter of water is placed in the flask, the apparatus 
connected up with the flask and the condenser, and heat 
applied to the bottom of the reservoir. The lower side open- 
ing k is opened, and the 
first portions of the ex- 
tractives are collected 
there. After the strong 
extractives have been 
removed, the side open- 
ing is closed and the 
cock / opened, and a 
cumulative extraction 
continued until extrac- 
tion is complete. 

29. In extracting 
sumac and similar ma- 
terials, which must have a 
cooler initial extraction 
temperatures, the cap 
can be left off and water 
at the desired temper- 
ature allowed to drip on 
the material, collecting extractives at either side opening. 
When the strong portions have been removed, the cap is 
replaced, connected with the condenser, the side openings closed, 
the cock/ opened, and the extraction completed with steam 
from the flask connected to the stem e. The materials men- 
tioned may also be extracted by covering them with cold water 
almost to the level of the upper side opening, connecting with 
condenser and reservoir, boiling the water in the reservoir slowly, 
and collecting the first portions at the upper side opening /. 




Fig. 6 



26 



MANUFACTURE OF LEATHER, PART 2 



When the desired amount of extractives is thus removed, the 
side opening is closed, the cock / opened, full heat applied to 
the reservoir, and extraction completed. 

In all cases where strong extractives are removed from the 
apparatus, they should be mixed while hot with the weaker 
extractives that have accumulated in the reservoir, the entire 

extraction allowed to cool, made up to 
1,000 cubic centimeters, and the analysis 
proceeded with. 



30. Remarks Regarding Determi- 
nations to Be Made. — Three determina- 
tions, the total solids, soluble solids, and 
non-tannins, are made in a tannin analysis, 
and from the results the insolubles, or reds, 
and the tannins are obtained. The differ- 
ence between the total-solids figure and the 
soluble-solids figure gives the amount of 
insolubles, or reds. By subtracting the 
non-tannin results from the soluble-solids 
results, the amount of tannins in the liquor 
is obtained. It is not necessary to dwell 
on the definition of these terms, but a few 
words on some of their constituents will 
not be amiss. 

31. The reds, or insolubles, have been 
defined under tanning materials. Because 
of their greater or less solubility in warm 
liquor, it is necessary that the analysis 
should always be made when the liquor 
has a temperature of from 60° to 70° F. 

If colder, the reds figure will be higher and the subsequent 
tannin result lowered; if warmer, the reds will decrease and 
the tannin content increase. 

Under non-tannins are classed all soluble substances in the 
liquor not absorbed by hide. For the most part, the non- 
tannins consist of sugary substances derived from the sap of 
the tree. In the same manner, under tannins are included 




Fig. 7 



MANUFACTURE OF LEATHER, PART 2 27 

all soluble substances that will combine with hide, thus embrac- 
ing all the forms of tannic acid. 

32. Determination of Total Solids. — When the liquor, 
extracted and prepared as has been described, has cooled to 
20° C, the cylinder a. Fig. 7, is shaken and allowed to stand 
for J hour; this is to allow small particles of bark to settle, so 
they will not be counted as reds, or insolubles proper. At the 
expiration of J hour, remove with a pipette 100 cubic centi- 
meters of the liquor, place in a weighed glass crystallizing dish, 
and evaporate to dryness in a combined evaporator and dryer. 
Cool in a desiccator and weigh. From this weight the per- 
centage of total solids is determined. 

33. Determination of Soluble Solids. — To determine 
the soluble solids, place 1 gram of kaolin in a beaker and add 
75 cubic centimeters of the tannin solution. Stir and pour on 
a pleated filter paper, collecting the filtrate in a clean beaker. 
Then return the filtrate to the paper for 1 hour, keeping 
the filter full. At the expiration of 1 hour, remove any of the 
solution remaining in the funnel and throw away both the 
solution and the filtrate. Refill the filter with the tannin 
solution, and as soon as the filtrate runs clear, collect it in a 
clean, dry beaker and remove 100 cubic centimeters for evapo- 
ration and drying. The kaolin should be previously washed 
with hydrochloric acid, then with distilled water, and finally 
dried and pulverized. It is used as an aid in filtering, form- 
ing a thin film over the paper, thus insiuing a clear filtrate. 
The paper and kaolin absorb tannin from the solution, so 
that the affinity of these for tannin must be satisfied by 
allowing them to be in contact with the tannin solution for 
1 hour before filtering the solution to be collected for drying 
and weighing. 

34. Preparation of Hide Powder for Determining 
Non-Tannins. — To determine the non-tannins, hide powder 
is used. Hide powder is made by liming and depilating 
selected steer hides, neutralizing the lime remaining in the 
hide, and washing out the excess of acid with water. The 



28 MANUFACTURE OF LEATHER, PART 2 

hide is then slowly and carefully dried without heat, and, 
when dry, it is ground about as fine as sawdust. 

To prepare hide powder for use, the almost universal practice 
is to chrome it slightly. The chroming treatment increases 
the rapidity of absorption of the tannins, and by combining 
with the chrome-tanning materials the soluble portions of the 
hide substance are rendered insoluble. The American method 
of chroming is first to soak the dry hide powder overnight in 
water and then squeeze out the soak water through a linen 
cloth. Fresh water approximating twenty-five times the weight 
of the dry hide powder is added, and chrome alum (in solution) 
to the amount of 3 per cent, of the weight of the dry hide 
powder is added and thoroughly mixed. The mixture is 
frequently stirred during the day, allowed to stand overnight, 
and washed the next morning by alternately squeezing through 
a cloth and adding fresh water until the wash water is free 
from sulphates. When thoroughly washed, the mass is placed 
in a press and squeezed until the wet hide contains between 
70 and 75 per cent, of water. It is then ready to be used for 
detannizing the tannin solutions. 

35. Determination of Non-Tannins. — ^For the non- 
tannin determination, measure 200 cubic centimeters of the 
bark liquor into a strong glass tumbler, such as is used with 
a milk-shake machine, and after weighing 20 grams of the wet 
hide, place the liquor in the steam oven and dry it for moisture 
determination. Weigh out from the press the amount of wet 
hide necessary for the determination of non-tannins. Place 
this in the liquor, breaking up the limips with a glass rod, and 
then shake the solution thoroughly. The shaking may be 
done by hand, using a tin cap such as is used for mixing 
drinks, or by a hand- or power-driven milk-shake machine. 
Shaking for 5 minutes on a milk shaker is sufficient for the 
hide powder to absorb every trace of tannin from the liquor. 
After shaking, add about 2 grams of kaolin and filter the 
solution through double filter paper. When the filtrate is 
running clear, collect, and with a pipette remove 100 cubic 
centimeters to a crystallizing dish ; evaporate, dry, and weigh 



MANUFACTURE OF LEATHER, PART 2 29 

in the same manner as when the percentage of solids was 
determined. 

The amount of hide powder to be used depends on the 
strength of the bark Hquor. In the case of unleached materials, 
the amount of sample extracted and the proportion of extrac- 
tion water should be such as to give between .35 and .45 gram 
of tannin per 100 cubic centimeters of extractive solution. 
If these specifications have been carried out, an amount of wet 
hide powder representing from 12 to 15 grams of the dry 
powder should be used for 200 cubic centimeters of solution. 
In extracting spent materials, it is seldom found possible to 
procure an extractive solution that will contain .35 to .45 gram 
of tannin per 100 cubic centimeters, but the proportion should 
be approximated as closely as possible, and the quantity of hide 
powder used should be decreased accordingly. 

Whether or not enough hide powder has been used, can 
generally be judged by the appearance of the non-tannin 
filtrate; if clear and white or pale yellow, the tannin has 
probably been removed. If the filtrate has a red or brown 
tinge, it is generally safe to assume the presence of some 
tannin. Doubtful filtrates should be tested with a 1-per-cent. 
gelatine to 10-per-cent. salt solution, cloudiness indicating the 
presence of tannin. 

36, Calculation of Results of Bark Analysis . — Divide 

the weight of the total-solids residue by the nimiber of grams 
of bark taken, and divide this result by the percentage of 
actual bark in the sample, found by subtracting from 100 the 
percentage of moisture, as determined in a 10-gram moisture 
sample. This result, when pointed off to correspond to the 
decimal part of the original liter, is the percentage of total 
solids. The percentage of total soluble solids is found in the 
same manner. 

Because of the water added by the wet hide used in the 
non-tannin determination, a correction must be made. If the 
20-gram sample of wet hide powder when dry weighs only 
6 grams, there are 14 grams of water added to the liquor for 
every 20 grams of wet hide used. If 40 grams of wet hide is 

39J— 6 



30 MANUFACTURE OF LEATHER, PART 2 

used, there are 28 grams of water added, and the volume then 
becomes 228 cubic centimeters instead of the 200 cubic -centi- 
meters originally taken; 100 cubic centimeters of the diluted 
filtrate has been dried, and it accordingly represents only 
YYT ^^ ^^^ actual amount of non-tannins, so the weight must 
be multiplied in this case by 1.14. Therefore, to calculate the 
percentage of non-tannins, divide the non-tannin weight 
successively by the nimiber of grams of bark taken and the 
percentage of dry bark, as under the solids calculations, and 
multiply this result by the hide-moisture correction. 

Illustration. — For the analysis, 25 grams of bark were taken and 
40 grams of wet hide powder were used. The bark contained 12 per 
cent, of moisture and 88 per cent, of dry bark. A 20-gram sample of 
wet hide when dried weighed 7 grams. The 40 grams of hide used, there- 
fore, contained 14 grams of dry hide and 26 grams, or cubic centimeters, 
of water, which latter was added to the original 200 cubic centimeters. 

= 1.13, or the hide-powder correction for moisture 

200 

Gram 

Total-solids residue weighed 4983 

Total soluble-solids residue weighed 4012 

Non-tannin residue weighed 1441 

For the total-solids determination, 100 cubic centimeters of liquor was 
taken, or .1 of the liter. The calculation would be as follows: 

.4983X100X10 , p , , 1 r^ 

=22.65 per cent, oi total solids 

25X.88 

The total soluble solids are calculated in the same manner. 

* = 18.24 per cent, of total soluble solids 

25X.88 

The total solids less the total soluble solids give the amount of insolubles. 
22.65-18.24 = 4.41 per cent, of insolubles 

For the determination of non-tannins, 100 cubic centimeters, or -j^ liter, 
of liquor was dried. The hide-powder correction was found to be 1.13. 
The calculation would be as follows: 

=1441X100X10X1.13 ^^^ .... 

= 7.40 per cent, ot non-tannins 

25X.88 

The total soluble solids less the non-tannins give the amount of available 
tannin. 

18.24 — 7.40 = 10.84 per cent, of available tannin 



MANUFACTURE OF LEATHER, PART 2 31 



The complete analysis is as follows 



Per 

Cent. 



^ , \ ... [Total soluble solids (^^^"^^^^^^^ J'^^ J18.24" 

Total solids < [Tannins 10.84 J \ 22.65 

[Reds, or insolubles 4.41 

Insoluble parts of bark (not removed by leaching) . . 77.35 



Total. 100.00 

This would be reported as follows : 

Per Cent. 

Moisture 12.00 

Total solids 22,65 

Soluble solids ] S.24 

Non-tannins 7.40 

Tannins 10.84 

Reds (or insolubles) 4.41 

37. . The figures in the preceding illustration are, of course, 
on an absolutely dry basis. If it were desired to report the 
results on the commercially dry basis, simply multiplying the 
absolutely dry figures by .88 would give the commercially dry 
figiu-es. The sample having contained 12 per cent, of moisture, 
there would, of coiurse, be 88 pounds of absolutely dry bark in 
every 100 pounds of the commercial article. 

It is customary to report fresh-bark results on the absolutely 
dry basis, and then give the tannin figtire also on the com- 
mercially dry basis. Spent-material results should be reported 
on the dry basis and cannot really be reported on the com- 
mercial basis unless the analysis of the original new material 
is known. This is because a considerable portion of a new 
bark is removed by the leaching process, and the analysis of 
the spent bark is not on the same basis as to bark weight as 
was the analysis of the original new bark. Taking this into 
account and figuring back the results to the same basis, the 
commercially dry tannin figure of a spent tan analysis is found 
to be about 77 per cent, of the absolutely dry tannin figiu-e. 



32 MANUFACTURE OF LEATHER, PART 2 



ANALYSIS OF TANNING EXTRACTS 

38. The exact conditions to which an extract analysis must 
conform, in order that it may be said to have been made by 
the Official Method, are set forth annually in the report of the 
American Leather Chemists' Association, which comprises 
practically all the leather chemists of the United States. As 
now carried out, the method is to dissolve a quantity of the 
extract as will give from .35 to .45 gram of tannin per 100 cubic 
centimeters of solution in 900 cubic centimeters of water at 
80° C, making up to the liter mark after standing not more 
than 20 hours and not less than 12 hours. The temperature 
of the solution must not go below 20° C. 

39. Total Solids. — Mix the solution thoroughly, and 
pipette 100 cubic centimeters into a tared glass dish. Evap- 
orate, dry, and weigh. 

40. Soluble Solids. — ^Place 1 gram of acid-washed kaolin 
in a beaker and add 75 cubic centimeters of the solution. Stir 
and pour on a No. 590 S. & S., 15 centimeters, pleated filter 
paper. Return the filtrate to the paper for 1 hour, keeping 
the filter full. At the expiration of 1 hour, potir the remaining 
solution from the filter or remove with a pipette. Then refill 
the filter with another portion of the solution brought to a 
temperature of 20° C, and begin to collect the filtrate as soon 
as it runs clear. Pipette 100 cubic centimeters of the clear 
filtrate into a tared glass dish, and evaporate, dry, and weigh. 
The funnels and receiving vessels should be covered to guard 
against evaporation. 

41. Non-Taniiiiis. — Add to 200 cubic centimeters of the 
solution a quantity of wet hide powder representing from 
12 to 15 grams of dry hide. Shake for 10 minutes and squeeze 
immediately through a linen cloth. Add 2 grams of kaolin to 
the filtrate, stir, and filter through a folded filter of size suffi- 
cient to hold entire filtrate, returning the filtrate until it is 
running clear. Evaporate and dry 100 cubic centimeters of 
this filtrate. The hide powder is to be prepared as previously 



MANUFACTURE OF LEATHER, PART 2 33 

described, and the non-tannin filtrate should be tested for 
tannin if its presence is suspected. 

42. Calculation of Results of Tanning-Extract 
Analysis. — The results are calculated by dividing the different 
weights by the amount of extract taken and pointing off for 
the percentage basis, not forgetting the hide-moisture correc- 
tion on the non-tannin weight. 



ANAIiYSIS OF TAN LIQUOR 

43. Determination of Specific Gravity and Total 
Solids. — Shake the sample well and with a barkometer 
determine its specific gravity in degrees barkometer. As a 
general rule, 1° barkometer represents .25 per cent, of total 
solids, and by applying this rule, the amount of liquor to be 
taken to make the proper dilution for analysis may readily be 
computed. The liquors should be diluted so that 100 cubic 

TABLE n 

AMOUNT OF HIDE POWDER REQUIRED FOR DIFFERENT 
TANNIN STRENGTHS 



Tannin Range 
per loo Cubic Centimeters 



•35 to 45 gram 
•25 to .35 gram 
.15 to .25 gram 
.00 to .15 gram 



Dry Hide Powder 
per 200 Cubic Centimeters 



8 to 10 grams 
5 to 8 grams 
2 to 5 grams 
o to 2 grams 



centimeters of the diluted liquor will give a residue approximat- 
ing .7 gram in weight. The water used for dilution should have 
a temperature of 70° P. After thoroughly mixing the diluted 
liquor, the total solids, soluble solids, and non-tannins are 
determined as under Analysis of Tanning Extracts. Since the 
dilution varies with the gravity of the liquor, the tannin 
strength of the different diluted liquors is not the same, and 
different amounts of hide powder are used, depending on the 
tannin content of the liquor. 



34 MANUFACTURE OF LEATHER, PART 2 

Table II shows what is believed to be the proper amounts of 
hide powder to be used for different tannin strengths. 

For convenience in calculating results, it is best to dilute 
the liquors to the volume of 1 liter. When thus diluted, the 
weights of the different residues divided by the niunber of 
cubic centimeters of liquor diluted to 1 liter will give a result 
that only needs proper decimal pointing to indicate the per- 
centage of each item. The moisture correction for the hide 
powder must be applied to the non-tannin weight. 

44, Determination of Total Free Acids. — There are 
several methods in use for the determination of the total free 
acids, but none is above criticism and results are comparative 
rather than absolute. 

Charcoal Method. — To 100 cubic centimeters of the diluted 
liquor used for the determination of the tannin, add 2 grams 
of chemically pure animal charcoal. Stir frequently during a 
period of 2 hoiu-s, strain on a dry filter, and titrate an aliquot 
portion with decinormal alkali, using phenol-phthalein indicator. 

Or, to 100 cubic centimeters of the diluted liquor in a flask 
with a tube condenser add 2 grams of the charcoal. Heat to 
boiling with frequent shaking; then cool, filter, and titrate an 
aliquot portion. 

Quinine Method. — Dilute 50 cubic centimeters of original 
liquor to 500 cubic centimeters. To 200 cubic centimeters of 
the diluted liquor, add 20 cubic centimeters of quinine solution. 
Mix thoroughly and filter. Take 100 cubic centimeters of the 
filtrate and titrate with decinormal alkali and phenol-phthalein 
indicator. Multiply the number of cubic centimeters used by 
.066 to obtain direct the percentage of acid, as acetic acid, in the 
original liquor. 

The quinine solution is made by dissolving 15 grams of 
quinine (pure alkaloid) in 110 cubic centimeters of 95-per-cent. 
alcohol that has previously been neutralized. To this, add 
slowly while stirring 90 cubic centimeters of distilled water, so 
as to bring the volume up to 200 cubic centimeters. 

Lime-Water Method. — Titrate 20 cubic centimeters of the 
original liquor, filtered, with twentieth normal lime water. 



MANUFACTURE OF LEATHER, PART 2 35 

The end point is indicated by the beginning of tiirbidity, when 
sufficient lime water has been added. Some chemists put the 
filtered liquor in a flat 2-ounce panel bottle, in which the panels 
are very close, and then titrate, holding the bottle against a 
strong light. 

45. Determination of Combined Sulphuric Acid. 

In acid tanneries, a determination of the free and combined 
sulphuric acid present in the liquors is frequently required. 
To determine the combined sulphuric acid, evaporate 100 cubic 
centimeters of the original liquor in a platinum dish and char 
the residue at a very low red heat. Cool, add hydrochloric 
acid and hot water, filter, and determine the sulphates in the 
filtrate with barium chloride, as explained in Quantitative 
Analysis. 

To determine the total sulphuric acid, take 50 cubic centi- 
meters of the original liquor, add distilled water and a little 
hydrochloric acid, bring to a boil, and precipitate the sul- 
phuric acid with barium chloride. The difference between 
the percentages of total acid and combined acid will be the 
approximate free sulphuric acid in the liquor. 

When the amount of free sulphuric acid only is required, a 
more accurate method is to evaporate 100 cubic centimeters 
of the liquor on a steam bath and digest the residue with 
absolute alcohol, determining sulphuric acid in the alcohol 
after digestion. 

46. Bleacli Liquors. — It is frequently desirable to know 
the amount of material removed from leather by the bleach 
baths. The following method gives fairly accurate figures: 

Take samples of all baths before starting the day's work 
and at the close of the day. Evaporate and dry 50 cubic 
centimeters of each sample, weigh, and subtract the combined 
morning percentages from the combined evening percentages. 
Multiply the difference in percentages by the weight of water 
in a single vat, and from the result subtract the weights of soda 
and acid added during the day (acid weights should be taken 
at 100 per cent, and sal soda weights at 40 per cent, actual 
solids) . The remainder will be the approximate amount of 



36 MANUFACTURE OF LEATHER, PART 2 

organic material removed in all the vats. When this figure is 
divided by the nimiber of sides bleached, the amount of solids 
removed from each side of leather will be obtained. 

A method of determining the amount of tanning material 
removed by the soda vat is to evaporate and dry 50 cubic 
centimeters of the liquor in a platinum dish, weigh, and then 
char the contents, break up the charred mass, add hot water 
and titrate. The difference between the weight of the dried 
residue and the weight of the alkali (figured in its form at the 
drying temperature), will give the organic matter in 50 cubic 
centimeters, and knowing the size of the vat and the n-umber 
of sides bleached, the amount removed per side may be readily 
calculated. 

ANALYSIS OF LEATHER 

47. For many reasons, it is frequently desired to determine 
quantitatively the constituents of different leathers, and while 
the analysis of leather is not difficult, yet, in order that different 
analysts may secure concordant results, it is necessary for them 
to follow identical methods in determining the composition of 
leather. 

The samples should be taken from different parts of the side 
of leather, since different portions of the leather will show a 
difference in composition, because of the difference in the 
thickness and texture of the hide. The belly and flank, being 
softer than the back, will make leather of an entirely different 
composition from that of samples taken from the back of the 
same side of leather. 

The samples are prepared by grinding, or by shaving with a 
carpenter's plane, or by the use of a coarse wood rasp. The 
finely divided leather should be well mixed and stored in a 
stoppered glass jar. 

48. Determiiiatioii of Moisture. — In determining the 
amount of moistm*e present, 10 grams of the ground leather 
should be dried for 1 hour in an oven at a temperature of 
105° C. This period of time will generally suffice to drive off 
moisture from most samples, but occasional samples require a 



MANUFACTURE OF LEATHER, PART 2 37 

longer time. After taking the dry weight, it is well to replace 
the sample in the oven and subject it to a further drying of 
15 minutes, weighing it again in order to verify the dry weight 
originally obtained. 

49. Determination of Ash. — ^For the determination of 
ash, 15 grams of the ground leather should be burned in a 
platinum dish. The leather should be slowly heated until all 
volatile matter is driven off; then the charred mass may be 
broken up and the ignition concluded. 

Mineral adulterations will be indicated by the analysis of the 
ash, and these are determined by a quantitative examination of 
the residue. Epsom salts are quite commonly used for bright- 
ening and tempering leather and also for adulteration, and if 
this material is the only constituent of the ash to be sought, 
its presence may be quickly determined by dissolving the ash 
in hydrochloric acid, precipitating iron and alumina with 
ammonia, and filtering. After precipitating and filtering off 
the lime, the magnesiimi is determined in the cooled filtrate by 
precipitation with sodium-ammonium phosphate. 

50, Determination of Oil. — To determine the oil and 
grease in leather, a 15-gram sample is extracted in a glass 
Soxhlet extractor for 3 hours, using about 100 cubic centi- 
meters of petroleum ether as a solvent. The petroleum ether 
should be tested by evaporating 100 cubic centimeters in a 
tared dish and weighing any residue. The oil extraction 
should be conducted by heating the flask on a steam bath, so 
that there shall be a constant ebullition of the petroletim ether 
and a steady drip of the condensed vapor falling on the leather 
in the Soxhlet apparatus. When extraction is complete, pour 
the ether (which should now contain the oil and grease originally 
in the leather) into a tared, glass crystaUizing dish, rinsing out 
the fiask with a little additional petroleum ether. After 
evaporating the ether, the oil residue remaining in the crystal- 
hzing dish is dried and weighed. To determine the nature of 
the oils or greases used, a larger quantity of the leather must 
be extracted in order that the oil residue may be sufficiently 
large to admit of qualitative and quantitative examination. 



38 MANUFACTURE OF LEATHER, PART 2 

51. Determination of Nitrogen. — The amount of hide 
substance in a leather is found by first determining the per- 
centage of nitrogen in the sample. From this figure the per- 
centage of hide contained in the leather is calculated by 
dividing by the factor .178. This factor is generally agreed 
on as the result of many analyses, which showed the average 
nitrogen content of hide substance to be 17.8 per cent. 

To determine nitrogen in leather, the oil in the leather must 
first be extracted, as the presence of fatty oils or greases would, 
of cotirse, give a fictitious nitrogen result. It is convenient to 
dry the residue from the sample used for determining the oil, 
making the nitrogen determination on this dried, oil-free 
sample. The method is practically the well-known Kjeldahl 
nitrogen method, some slight modifications being made in its 
operation. Of the dry, oil-free sample 1.5 grams is weighed 
into a Kjeldahl flask, and 20 cubic centimeters of strong 
sulphuric acid and 1 drop of metallic mercury added; the 
mercury is added to help in the oxidation of the carbonaceous 
matter. A loose-fitting, hollow balloon stopper is placed in 
the neck of the flask, and the flask is then held in a sloping 
position over a low flame that is gradually increased, and the 
contents are allowed to boil slowly until nearly colorless. 
While still hot, drop in crystals of potassiimi permanganate 
until the solution remains slightly purple. Then transfer it to 
a distilling flask with 300 cubic centimeters of water, add 
25 cubic centimeters of potassium-sulphide solution (40 grams 
to liter) , and connect the flask with the water condenser, being 
careful to have all joints absolutely tight. 

The distilling flask should be provided with a double-per- 
forated stopper, one perforation for the tube leading to the 
condenser, and the other for the stem of a separatory funnel. 
After passing through the water-jacket, the delivery tube 
should be connected by means of a tight -fitting, perforated 
cork, to one leg of a large, bulbed U tube containing 50 cubic 

centimeters of — sulphuric acid. The U tube is set in a larger 

beaker about half full of cold, neutral, distilled water. After 
connecting the distilling apparatus, a strong solution of sodium 



MANUFACTURE OF LEATHER, FART 2 39 

hydroxide is placed in the separatory funnel, and by gradually 
opening the cock, an excess of the solution is run into the 
flask and the cock closed. Heat is then appHed to the flask 
and slow distillation continued for about 30 minutes. The 
ammonia released by the addition of the alkali passes over 

through the condenser and is absorbed by the — acid in the 
U tube. When the distillation is complete, the acid in the 
U tube is titrated back to neutrality with — ammonia, using 

cochineal as an indicator. The water in which the U tube has 
been immersed should always be titrated in case the U tube 
has overflowed. The amount of standard ammonia used in the 
titration, deducted from 50 cubic centimeters, gives the quantity 
of acid neutralized by the ammonia from the leather, each 
cubic centimeter of which corresponds to .017 gram of 
ammonia, or .014 gram of nitrogen. The percentage of nitrogen 
divided by .178 gives the percentage of hide fiber in the leather. 
The reagents used must be free from ammonia, and a blank 
test, using sugar, should be made, making correction, if neces- 
sary, on subsequent determinations of nitrogen in leather. 

5 2 . Det erminatlon of Water- Soluble Materials . — The 

estimation of the amount of water-soluble materials in leather 
presents the only mechanical difficulties encountered in the 
extraction of the leather. The total amount varies with the 
period of extraction, although after a certain time the remaining 
solubles are not appreciable. The ground leather may be 
extracted by simple digestion with successive quantities of water 
at 40° to 50° C, squeezing the mass in a linen cloth after each 
digestion and then adding fresh water. This kind of extraction 
results in a large volume of weak extractive solution, which is 
sometimes concentrated by boiling, so that the entire volume is 
reduced to 1 liter. If only the total amount of water solubles 
is desired, this procedure is not objectionable; but when the 
constituents of the water-soluble matters are to be determined, 
concentration by boiling should be avoided. Probably the 
best method of extraction is to digest the sample three or four 



40 MANUFACTURE OF LEATHER, PART 2 

times with water at from 40° to 50° C, then transfer the mas^ 
of leather to a glass Soxhlet, and complete the extraction, 
uniting the extractives secured by the two methods. The 
boiling temperature necessitated by the Soxhlet extraction will 
cause the leather to run together and form a sticky mass, 
through which the extracting water can pass only with difficulty. 
This may be prevented to some degree by mixing the leather 
with several times its volume of sand before placing it in the 
extractor. For the water-soluble determination, 20 grams of 
the sample should be extracted, as just outlined, and the 
extractive solution brought to a liter in volume. This is then 
analyzed for tannins and non-tannins, according to the methods 
of tan-liquor analysis previously described. 

53. Determination of Glucose. — Glucose in leather is 
determined in the water-soluble material by Fehling's solution 
after removing the tannin. The tannin is removed by basic 
lead-acetate solution, which is made as follows: 300 grams of 
lead acetate is mixed in a liter flask with 100 grams of litharge 
and 50 cubic centimeters of water. The flask is then heated on 
a boiling-water bath until the mixtiu-e is nearly white, more 
water being put in the flask to replace that which has evaporated. 
The mixtture is then digested with 1 liter of cold water and 
filtered. 

The lead-acetate solution having been made, 20 grams of 
the leather is digested with successive small portions of water, 
filtering after each digestion through a cotton plug stuck in 
the neck of a funnel. The temperatiu-e of the extracting 
water should be gradually increased from 40° C. for the first 
digestion to boiling water for the last two digestions. The 
extractive solution should amount to 500 cubic centimeters, 
and after cooling, 30 or more cubic centimeters of the basic 
lead-acetate solution is added, well mixed by shaking, allowed 
to stand for 15 minutes, and then filtered through a dry filter, 
collecting exactly 400 cubic centimeters. To the 400 cubic 
centimeters of filtrate add 30 cubic centimeters (or more if 
necessary to throw out the lead) of a strong magnesiiun- 
sulphate solution, shake, and filter on a dry filter. Boil 



MANUFACTURE OF LEATHER, PART 2 41 

100 cubic centimeters of this filtrate with 3 cubic centimeters 
of strong hydrochloric acid for 3 hours, not allowing the 
volume to go below 75 cubic centimeters. This is for the 
purpose of inverting unconverted dextrin and intermediate 
products, which are generally present in commercial glucose 
and which, unless inverted, are not determined by Fehling's 
solution. 

After boiling, make the solution slightly alkaline by the 
addition of a concentrated sodium-hydroxide solution; make 
up to 100 cubic centimeters and filter if necessary. Transfer 
the solution to a clean burette and use it to titrate 10 cubic 
centimeters of Fehling's solution. For this operation 5 cubic 
centimeters of each of the Fehling solutions are placed in a 
casserole, 40 cubic centimeters of water added, and the whole 
brought to a boil. Run in from 5 to 10 cubic centimeters of 
the sugar solution at a time, boiling the liquid 2 minutes 
between each addition, until the blue color has nearly dis- 
appeared. The sugar solution should then be added in smaller 
quantities and the time of boiling reduced to J minute between 
each addition from the burette. The end point may be 
determined by the absence of blue color on looking through 
the supernatant liquor, or potassium ferrocyanide may be used 
as an indicator. If the indicator is used, take a few cubic 
centimeters of the solution, run through a very small filter, 
and add a little acetic acid and 1 drop of potassiiun-f errocyanide 
solution. 

54. It is well to make an approximate titration at first 
and then a second titration on another 10 cubic centimeters 
of Fehling's solution, adding nearly the whole of the required 
sugar solution at once, so that the time of boiling and titration 
is reduced to a minimum. Fehling's solution, of which 10 cubic 
centimeters equals .05 gram of glucose, is made in two parts as 
follows : 

In making solution 1, dissolve 34.6 grams of pure crystal- 
lized copper sulphate in distilled water, then add 10 cubic 
centimeters normal sulphuric acid and make up the whole to 
500 cubic centimeters. 



42 MANUFACTURE OF LEATHER, PART 2 

In making solution 2, dissolve 125 grams of chemically pure 
potassium hydroxide and 173 grams of pure potassium sodium 
tartrate (Rochelle salts) in distilled water and make up to 500 
cubic centimeters. 

To make Fehling's solution, 5 cubic centimeters of each of 
these solutions are mixed just before using. 

A convenient strength of the magnesium-sulphate solution 
is made by titrating 10 cubic centimeters of the basic lead- 
acetate solution with a strong solution of magnesitim sulphate 
until no ftirther precipitate is produced. One hundred times 
the quantity of sulphate solution needed for the titration is 
made up to a liter, and the use of this solution will result in the 
removal of the lead without a large residual excess of magnesiimi 
sulphate. 



MANUFACTURE OF LEATHER 

(PART 3) 

Serial 416C Edition 3 

LIMP, OR LIGHT, LEATHERS 



PROCESS OF MANUFACTURE 



1. Introduction. — In order to make a soft and pliable 
product known as limp, or light, leather, the hides or skins 
used require very much different treatment from that given 
to the hides in the manufacture of sole leather. The actual 
tanning for certain classes of leather is conducted along the 
same general lines as in the making of sole leather, but with 
weaker liquors and covering a shorter period of time. With 
these pliable leathers the tanning is really the smallest part 
of the manufacturing process, as the finishing of the leather 
requires a larger proportion of time and labor. The tanning, 
however, whether it be vegetable, mineral, or oil, must be 
suited to the use for which the leather is intended, as no 
amount of skilled finishing can entirely obliterate the defects 
of an improperly tanned hide. Because of the multiplication 
of operations in making li,8:ht leathers, processes of manu- 
facture differ to a greater extent than in the tanning process 
for heavy leather. Every light-leather tanner aims to attain 
the same result, but methods differ in each department of 
different tanneries; and nearly every tanner uses methods 
and formulas differing slightly from the methods and for- 
mulas of his competitors. 

As they appear on the market, limp, or light, leathers 

COPYRIGHTED BY INVERNATIONAL TEXTBOOK COMPANY. ALL RIGHTS RESERVED 



2 MANUFACTURE OF LEATHER, PART 3 

may have been made from whole hides or skins, or they may 
have been made by spHtting heavy hides into a number of 
Hghter pieces, or splits. The tannage of these hides, spHts, 
or skins varies according to whether they are to be used for 
automobile leather, shoe leather, bag and strap leather, fancy 
leather, or glove leather. No general description can be given 
to include all classes, although some of the steps may be 
similar for the different grades. 

In discussing light leathers each class will be taken up indi- 
vidually and, when possible to do so, reference will be made 
to like treatment in other branches of the industry. 

As Part 1 deals entirely with heavy leather of vegetable 
tannage, we will first consider the light leathers which are 
also of vegetable tannage, and then follow with mineral and 
oil tannages. 



AUTOMOBILE AND UPHOLSTERING 
LEATHERS 

2. General Preparation. — In making leathers for auto- 
mobile, carriage, and other upholstering purposes, the heavi- 
est and most spready of green salted hides are used, in order 
to make one hide cover the greatest possible surface. Swiss 
and Paris hides are popular for such purposes, and hides from 
these sources are largely made into leather for this class of 
work. The hides are soaked, fleshed, limed in straight lime 
solutions, unhaired, and bated. (See Part 1.) 

The bating of hides for automobile leather should be very 
complete, as the stock must be in as soft and open a condition 
as possible. Formerly manure bates were employed, but 
today either oropon, a material composed of ammonium 
chloride, wood fiber, and dry pancreas, or puerine is used. 
In using oropon, the paddle is about three-fourths filled with 
water at a temperature of 95° F. and about one-half of one 
per cent, of oropon on the weight of the stock is introduced. 
While the paddle is running, the hides are entered and the 
stock turned until all lime has been removed. The grain will 



MANUFACTURE OF LEATHER, PART 3 



by this time have assumed a silky condition and the fiber is 
probably well separated. 

In order to set the grain, secure a good, even color and 
obviate the danger from kiss spots, the stock is usually 
transferred from the bate to a spent tan liquor made acid 
with a small quantity of either an organic or a mineral acid. 




Fig. 1 

When ready for tanning, the hides are hung by the butt 
on a rocker frame and rocked in the tan liquor. The hides 
go into the weakest liquor, the stronger liquor gradually 
working through the section of rockers until the leather receives 
the strongest liquor and is sufficiently tanned for the split- 
ting machine. The tanning liquor is composed of a combina- 
tion of two or more tanning agents, such as hemlock, oak, 
quebracho, gambier, and palmetto. When the leather is suffi- 

393—7 



4 MANUFACTURE OF LEATHER, PART 3 

ciently tanned, the hide is run through a wringer, or piles of 
them are pressed in a hydrauHc press, to remove the excess 
of tan Hquor previous to spHtting. They are worlced on a 
stoning jack to remove wrinkles and to smooth out the surface. 

3. Stoning: Jack. — The stoning jack, shown in Fig. 1, 
is built of iron and is run by a side-belt drive. By means of 
a crank-shaft, an arm a supported and guided by a swinging 
truss is given a backward and forward motion, following the 
contour of an inclined metal bed h, the face of which is 
smooth and cut in the form of a segment of a circle. To the 
end of the arm is attached the stone c, which is a rectangular 
piece of metal with rounded corners and slightly longer than 
the width of the bed. When in operation, this tool is carried 
backwards and forwards over the bed at a distance from it 
regulated by the operator by means of a foot-lever. The 
leather is thrown on the face of the bed, under the moving 
arm, and the stone brought down on it. By the action of 
the stone the wrinkles and creases are removed, the leather 
being moved around under the stone by the operator, so that 
every part comes in contact with the stone, or smoothing 
tool. The grain side is finally split, the split being made 
light or heavy, according to the purpose for which the finished 
leather is to be used. 

4. Splitting: Macliines. — Two general classes of split- 
ting: macliines are in use, the Union splitter and the belt- 
knife splitter. . The latter is the more popular machine and 
is found in most of the Eastern upper-leather tanneries. 

In the Union splitter, the leather is presented to the 
edge of the splitting knife by gripping and drawing rollers. 
It is held on the rollers by carrying arms and is split by 
the power that rotates the roller by which the leather is carried. 

The belt-knife splitter, shown in Fig. 2, effects the split- 
ting by means of an endless belt knife a, against which the 
leather is carried by means of rolls. Machines of this type 
are not automatic, but require skilled labor to operate them 
economicallv. 



MANUFACTURE OF LEATHER, PART 3 5 

After having taken off the grain split the remainder of the 
hide passes under the eye of the inspector, who decides the 
number and weights of succeeding spHts. The grain sphts 
are then retained in revolving tight drums with quebracho 




and gambier liquors, the flesh splits being retanned in open 
vats, into which revolving paddle wheels dip. 

After retanning, the splits are run into a v/heel with sumac 
liquor, and after this treatment they are set out by hand or 



6 MANUFACTURE OF LEATHER, PART 3 

by machine to remove the excess of water, and while on the 
table they are given a mixture of degras and cod oil. The 
leather is then closely tacked to heavy frames clamped in a 
stretching machine wherein the wet leather is stretched in all 
four directions. The frame is then tightly clamped to retain 
the stretch, and it is taken to the drying loft, where the 
leather dries, retaining the increased surface given it by the 
stretching. When dry, the splits are broken by hand or by 
machine to make them soft and pliable, and after buffing, if 
necessary, they are ready for an application of the coating. 
The grain splits are hand-bufifed before being coated; machine 
buffing is also done by taking a very thin split from the grain. 

5. Daubing-. — The daub, or coating, for the leather 
is generally made by boiling down linseed oil with the desired 
pigment and thinning the mixture with naphtha. It is quite 
important that this daub should be properly made, and 2 days 
is generally required for the operation. The oil is boiled in 
a large kettle over a coke fire and constantly stirred. On 
the first day the temperature of the oil is run up to nearly 
600° F. and then lowered to about 380° F. before it is left 
for the day. On the second day, the temperature is raised 
a little over 600° F., and the cooking is continued until the 
desired consistency is attained. The oil is gradually cooled, 
the fire extinguished, and naphtha added to thin the jelly- 
like residue ; the naphtha is added in small portions with 
constant stirring. The highest grade of pigments that have 
been carefully ground in oil are thoroughly incorporated into 
the daub. All colors of coatings, different degrees of gloss, 
and varying thicknesses of the enamel are given to leather 
intended for different purposes. 

The grains, splits, and buffings having been assorted and 
assigned to the different grades, weights, and classes of fin- 
ished product, are stretched and tacked to frames and receive 
a heavy coat of the daub, which is carefully and evenly applied, 
the excess being removed. When the first coat has dried, a 
second coat is applied and the frames are placed horizontally 
in the drying oven, where the second coat is dried at a 



MANUFACTURE OF LEATHER, PART 3 7 

temperature of about 120° F. When this second coat has 
dried, a thinner coat of the boiled oil is applied, and after 
this has dried, the surface is smoothed by rubbing with pumice 
stone. From four to eight coats of the bottom daub are 
applied, according to the requirements of the finished leather, 
and the drying may be done either in the air or in the oven, 
depending also on the future use of the leather. When the 
bottom coats have been applied and the surface smoothed, a 
coat of varnish and oil is applied and dried in the oven. This 
may be followed by smoothing and the application of a final 
coat of varnish and oil, and after drying in the oven, and a 
sun-and-air drying to remove the stickiness, the leather is 
taken from the frames, trimmed, and is then ready for the 
market. Some of the heavy leathers, as, for instance, the 
visors for military caps, are coated on two sides, each with 
a different color. 

Various compositions other than boiled linseed oil are now 
being used for coating the leather, particularly for furniture, 
fancy embossed leathers and shoe leathers. Wood alcohol, 
amyl acetate, acetone, and other solvents are used as vehicles 
for carrying organic gums, pyroxylin, camphor, etc., in mak- 
ing up coats for shiny leather. 

6. Furniture and ornamental leathers receive fewer coats 
than the heavier carriage dash and automobile leather, and 
they are given a grain either by boarding, by pebbling, or by 
the embossing press. The newer compositions for coating 
are frequently used on this leather. 

The buffings, or grain splits from machine buffing, are 
very thin and are used for bookbinding and for covering 
boxes, etc. They are coated, colored, and surfaced and may 
be embossed. 

The popular so-called Spanish leather that is now frequently 
used in upholstering for mission furniture is made by tanning 
the hides in strong quebracho liquor, which draws the grain 
and gives the leather its unique appearance. In finishing, it 
is dyed to the desired shade and coated so that the pigment 
fills the wrinkles in the surface and accentuates the irregular 




/ i 



MANUFACTURE OF LEATHER, PART 3 



9 



grain. Spanish leather is also made by embossing the leather 
and then staining. 

7. Embossing. — For embossing, a heavy pressure, dis- 
tributed over a large area of leather, is needed. The emboss- 
ing machine shown in Fig. 3 consists of two geared rolls a 
and b. The lower one b is smooth and forms a supporting 
surface for the leather that is to be embossed. The upper 
one a is smaller, and the design to be embossed is cut in its 
surface. The leather is fed between the moving rolls and 
receives the design 

from the upper roll. 
The pressure is reg- 
u 1 a t e d by hand 
wheels c and d at 
either end of the 
machine , and a 
foot-treadle e, con- 
nected with clutch / 
on the drive shaft, 
assures perfect con- 
trol of the machine 
by the operator. 

8. A large pro- 
portion of the grain- 
ing and embossing 
of leather is done 
by embossing 
presses similar to 
the machine illus- 
trated in Fig. 4. 
A plate in which the pattern of grain or embossing desired 
on the leather has been cut is attached to and covers the 
bottom of the heated head a. The leather is laid on the 
bed b, and the lever d sets in motion the gears that raise 
the bed along the guide rods c until the leather comes in 
contact with the embossing plate on the head. The leather 
is subjected to enormous pressure, giving it the impression 




Fig. 4 



10 MANUFACTURE OF LEATHER, PART 3 

of the particular pattern on the plate. The bed is then 
automatically lowered, and another portion of the leather is 
moved on the bed to receive the pattern. The head may be 
heated by gas, steam, or electricity. 



BAG, CASE, AND STRAP LEATHER 

9. Vegetable-tanned leather for bags and straps is made 
from green salted hides. The hides are soaked and split into 
sides after coming from the soaks. They are then limed, 
unhaired, fleshed, and bated. After bating, the sides are 
attached to sticks and go into the rockers. The rocker liquors 
contain sufficient fermentative acids to neutralize any lime 
not removed by the bate, and to plump the sides. The small 
amount of tannin present serves to color the stock and prepare 
it for the subsequent tan liquors. After the rocker treatment, 
the hides are moved to the weakest of a series of vats con- 
taining progressively stronger liquors. The hides are moved 
forwards throughout the series until the strongest vat is 
reached. After hanging in the last vat the required length of 
time, the tanning is completed to the required degree. The 
time required for the tanning varies in different yards, being 
as low as 15 days in some and as high as 30 days in others. 
As the sides are to be split, complete tanning is not necessary, 
but it is essential that the sides should be colored entirely 
through, so that the splitting knife will have a homogeneous 
substance on which to work. The liquors are made by com- 
bining hemlock and oak barks, myrobalans, chestnut, and 
quebracho extracts in proportions < determined by cost, char- 
acter of leather desired, and the ideas of the tanner. 

10. After tanning, the sides are taken to the wringer and 
the excess of moisture removed. They are then smoothed 
out on the stoning jack, when they are ready for the splitting 
machine. After splitting into as many splits as the thickness 
of the side allows, or as the desired weight of the leather 
which is being made, requires, the splits are trimmed by hand 
and may be taken to the shaving machine for smoothing and 



MANUFACTURE OF LEATHER, PART 3 11 

to remove any humps. The splits are then retanned in a 
revolving drum, or wheel, with extract liquor. Some of the 
liquors which are in common use for this purpose are que- 
bracho, cutch, gambler, and palmetto extracts. The wheel 
treatment requires from -J to 2 hours. From the retanning 
wheel, the splits are carefully spread out and piled, the piles 
when completed being covered with canvas and allowed to 
stand from 24 to 48 hours, so that the liquor received in the 
wheel may complete its combination with the hide substance. 
After retanning, the leather is cleared by being run in a 
revolving drum, first with water, then with a solution of 
borax, then water, then a weak solution of sulphuric acid, 
and finally with another water, each solution being removed 
before the next solution is added. After clearing, the splits 
are run in a wheel with a sumac liquor, and occasionally 
some of the oiling is done in this wheel. The leather is 
then sorted and different grades assigned for different colors 
and for different purposes. The grain splits showing no hide 
imperfections are finished in the natural color for the best 
grades of leather. When the grading is finished, each lot of 
leather is dyed the assigned color, the dyeing being done 
either in a vat with a paddle wheel or in a tight drum. 
Leather to be dyed on one side only is, of course, colored by 
hand or by the blackening machine. 

11. After dyeing, the leather is hung over sticks to 
harden, or it may be worked out and the excess of moisture 
removed by the machine. When properly tempered, the 
leather is worked and oiled by hand on a table. The table 
is swabbed with oil, the split being laid on it grain side up. 
After working out the excess of water and breaking or soft- 
ening the leather, the grain is lightly swabbed with oil and 
then tacked on the drying frames and dried. When dry, it is 
removed from the frames, moistened to the proper degree, 
and a light oiling or a seasoning applied. The leather is then 
thrown over wooden horses and allowed to temper, and may 
receive subsequent treatments with either seasonings alone 
or seasonings containing dyes, to bring the color to the desired 



12 MANUFACTURE OF LEATHER, PART 3 



shade. After the seasoning treatment is completed, and when 
properly dried, the leather is surfaced on a surfacing machine, 
and may be finished with a glassing machine. It is then 
boarded by hand to break the leather, complete and make 
permanent its limp character, and give it a particular style 
of grain, if desired. This is done by light pressure on the 
cork-faced boarding tool strapped to the arm of the operator, 
the leather being doubled and the tool moving over the fold 
of the leather. Different degrees of dampness and different 
ways of operating the board result in different grain surfaces. 

12. If the leather is to be embossed in imitation of any 
grain desired, the embossing is done before or after the 
machine surfacing. The leather should be properly damp- 
ened, and, after embossing, it is dried and boarded. If the 
leather is to be blacked, the blacking is applied after season- 
ing. Three coats of any amyl acetate black are given, one 
coat being allowed to dry before the next is applied. 

It may be finished smooth or may be dampened and 
embossed in imitation of seal, or any desired grain, after 
which it may be run through a splitting machine to produce 
the particularly light leathers used for card cases, for covering 
boxes, or for decorative purposes, etc. 

The grain split from the hide is made up into the better 
grades of bag, strap, and fancy leather, while the flesh splits 
are generally used for cheap bag and strap leather, rough 
gloves, and innersoling. The flesh splits are frequently dyed, 
finished, and embossed, and sold for grain leather. 

13. For certain kinds of strap leathers, also harness and 
belting leathers, where strength is the principal requisite and 
a slight darkening of the color is not objectionable, it is 
customary to fidl the leather with a large amount of oil, the 
amount of oil and grease introduced often running as high 
as 45 per cent, of the weight of the finished leather. The 
material and processes employed are as follows : 

14. Stuffing- Materials. — The treatment of leather m 
such a manner that it will contain an amount of grease or oil 



% 



MANUFACTURE OF LEATHER, PART 3 13 

such as its future use may require is called stuffing. Stuffing 
is done both by hand and by machine, largely by the latter 
method. The former is used only on certain classes of leather. 

For stuffing leather, the oil par excellence is cod-liver oil. 
It has been in use since the early days of the industry, and as 
yet no other oil has been found that can satisfactorily displace 
it. Cod-liver oil has a good body and remains in practically 
the same state in which it entered, thus giving to the leather 
a permanent mellow feeling. 

This oil is expensive, and therefore substitutions are com- 
mon. Seal, menhaden, and mineral oils are commonly used 
for this purpose. 

It is almost impossible, with any marked degree of cer- 
tainty, to detect the fish oil when mixed with cod-liver oil. 
Fish oils have more gum than the genuine cod-liver oil; but 
cod-liver oil and menhaden oil have the same color and gravity, 
and their range of odor and taste is about the same. 

Menhaden oil, when cold pressed to remove the foots, is a 
good substitute for the average grade of cod-liver oil. 

Stearin, tallow, beeswax, Japan wax, and paraffin wax 
are all used for stuffing certain kinds of leather. 

Heavy refined mineral oils are largely used for mixing with 
cod and fish oils for stuffing heavy leather. 

Neatsfoot oil is used with satisfaction if a good cold-tested 
oil is secured; otherwise, a cold temperature will congeal 
the oil and thus turn the skin white. 

Sod oil is largely used for stuffing. It is pressed out from 
skins, and is ready for use after boiling and undergoing 
clarifying treatment. 

Degras is the oil obtained from wool during its cleansing 
process. French degras is the surplus oil obtained in the 
manufacture of chamois leather. It is frequently adulterated 
and is put on the market in all grades. 

Glycerine is used by some tanners instead of degras. It 
imparts to the leather a high degree of softness, but it should 
not be used alone, as it possesses a corrosive action and, being 



14 MANUFACTURE OF LEATHER, PART 3 

soluble in water, is easily removed from the leather by damp- 
ness. 

Porpoise oil is much valued for stuffing. 

Wool fat, obtained from the solvents used after extracting 
wool, is sometimes used as a substitute for degras. 

Olive oil is used in leather dressing, particularly in alum 
tannage. 

Castor oil is largely used, especially in its sulphonated form, 
known as Turkey-red oil, which is made by treating cooled 
castor oil with successive small portions of strong sulphuric 
acid. After standing, the oil is separated with salt solution 
and carefully neutralized. 

Sperm oil is occasionally used in finishing leather, and it is 
sometimes used in fat liquors. 

The yolks of eggs are used in stuffing high-grade glove 
leather, as it contains about 30 per cent, of an oil known as 
egg oil. 

15. Hand Stuffing. — In hand stuffing, the leather must 
be in a damp condition and the daubing mixture consisting usu- 
ally of cod-liver oil and tallow, is applied to the flesh. By means 
of a heavy slicker, the hides are worked on the table and then 
placed in piles in a warm room. The operation is repeated 
several times or until the necessary amount of oil has been 
introduced. As practiced, the operation of hand stuffing con- 
sists of rolling the sides into bundles, with the grain side in, 
and softening by heating; then the warm oil and tallow is 
applied with a brush to the flesh side. 

16. Drum Stuffing. — In the drum-stuffing method, 
the stuffing is effected by placing the hides and stuffing material 
in a revolving drum a. Fig. 5. The hides are dampened 
thoroughly on both sides and allowed to lie in a pile, which 
is then covered with damp cloths. The drum is heated by 
steam or hot air for some time before receiving the stock. 
The heat is turned off and the hides placed in the drum, which 
is then run for some time with the door loosely closed. This 
operation loosens up the goods and regulates the temperature. 
The stuffing material is then run in hot, but not hot enough 



MANUFACTURE OF LEATHER, PART 3 



15 



to scald the hides. The tight door is put on the drum and 
the stock wheeled for from i to 1 hour. The drum is stopped 
and the door opened, and the drum is then slowly revolved 
for a few minutes. The hides are finally taken out, smoothed, 
and laid in piles. 

They are generally stoned as soon as possible on marble 
or plate-glass tables (it is best to stone on the grain side 
first) and then hung up until nearly dry. The operation is 
repeated on the flesh side, removing all marks of the stone, 
after which the sides are again hung up until quite dry. There 




Fig. 5 

are several patented forms of stuffing drums in which the heat- 
ing is effected by means of coils containing steam or hot air. 
The coils keep up the temperature of the drum while the stuf- 
fing is going on and do away with the water of condensation. 
A hot-air stuffing mill is shown in Fig. 6. The air for the 
drum a is heated by steam coils in the heater b, from vv^hich 
the heated air is forced into the stuffing drum by means of a 
small fan blower, as indicated. 

17. Fat-Liquoring-. — For certain kinds of vegetable- 
tanned leather, especially light leather, the oil and greases are 
replaced by so-called fat liquors. These fat liquors are simply 
emulsions of different oils, fats, and soaps, the character of 



16 MANUFACTURE OF LEATHER, PART 3 

which depends on the kind of leather and its future use. 
Egg yolk is an example of a natural fat liquor. For some 
leathers, a fat liquor made up of water, olive-oil soap, olive 
oil, degras, and Turkey-red oil, is used. Some tanners use 
a mixture of water; neatsfoot oil, glycerine, and castor-oil 
soap, and there are many other combinations of soaps and 



Fig. 6 



oils used for fat liquors. The preparation and use of fat 
liquors is a part of the finishing process that has a marked 
influence on the softness and durability of the leather produced. 
Fat liquoring is done in a regular stuffing drum and the fat 
liquor added continuously during the revolution of the drum. 

18. Buffing, or AX^liitening-. — The buffing, or whiten- 
ing, required in the manufacture of some classes of leather 



MANUFACTURE OF LEATHER, PART 3 17 

is done either by hand or by a huffing, or whitening, machine. 
If done by hand, the leather is laid either on a table or on 
an inclined beam, similar to the beam used in the beam house, 
and buffed by scraping with a broad buffing tool. 

19. Wliitemng- Machine. — Whitening by machinery is 
effected by a machine, shown in Fig. 7, consisting of a rapidly 




Fig. 7 



revolving cylinder on the end of an arm having a pendulum 
motion. The face of the cylinder is covered with parallel 
knives, or spines, running transversely. The leather is laid 
on a bedplate under the moving arm, and the arm, with the 



18 MANUFACTURE OF LEATHER, PART 3 

cylinder, is lowered by means of a foot-treadle until it comes 
in contact with the leather. The pressure of the tool on the 
leather is regulated by the operator, who keeps the leather 
moving so that one section of the surface does not receive 
more of the abrasive action of the cylinder than another. 

The whitening machine illustrated is made of iron. The 
rotary cylinder, or whitening tool, a is driven by belts at either 
side and running on a small countershaft fixed in boxes at 
the end of the supporting double truss, or pendulum, d. The 
belt running the countershaft passes between the parts of the 
truss and over a pulley at its upper end, and thence to the 
main driving belt. The pitman e is connected with the balance 
wheel f, and from it receives a backward and forward motion. 
The foot-treadle b is for regulating the distance between the 
cylinder and bedplate c, and, accordingly, the pressure on the 
leather. The bedplate is of polished brass, is slightly wider 
than the cylinder, and is inclined. A revolving emery wheel g 
travels constantly from one edge of the revolving cylinder to 
the other, keeping sharp the faces of the knives, or spines of 
the cylinder. 



SIDE LEATHERS 

20. Splits. — Leathers made from split cow and steer hides 
tanned by a vegetable-tanning process are used to a large 
extent in various grades of shoes. The same conditions as 
to varieties exist with this class of leather as with other 
classes. The hides are usually split out of the lime, the grain 
going into mineral tannage while the split is vegetable-tanned. 
This flesh-split is used largely for cheap shoes as brogan 
leathers, are stuffed in the drum and then grained or waxed 
as desired. 

The splits from side leathers are also sometimes given a 
pyroxylin finish and are known as dope splits. 

When the splits are to be finished for cheap shoe leather 
the stock after stuffing is cleaned smooth by working on the 
whitening machine after which it is ready for the color. 




19 

393—8 



20 MANUFACTURE OF LEATHER, PART 3 



21. Blackening-. — After whitening, or buffing, the leather 
is ready for blackening. For the heavy grades of upper 
leather, this operation is preferably done by hand. The liquid 
blacking or other dressing to be applied to the surface of the 
leather is spread evenly over the hide by means of oval 
brushes made of fine bristles. The excess of blacking is 
removed by other brushes, care being taken that no blacking 
reaches the under side of the leather. 

22. Blackening Macliine. — A popular machine for 
blackening leather is the Batchelder, shown in Fig. 8,' or 
modifications of it. In this machine, the leather is spread 
on the table a and fed into the machine. The edge of the 
leather is engaged between the surfaces of two rolls and then 
passed over a third roll, which forms a supporting bed for 
the skin, while the brush b applies the blacking. The black- 
ing or other dressing is in the receptacle c, and the fluted 
roll c' running at the edge of the blacking receptacle supplies 
ihe brush with the coloring matter. The brush d seems to 
work the blacking into the leather and also to remove any 
excess. After passing under the second brush over the sup- 
porting roll d', the leather is delivered to a moving bed e, 
formed by endless tapes extended around rollers / and /' 
and driven by gears. 

As the hide does not always cover the roll supporting it 
under the blacking brush, some blacking reaches the roll. 
This roll must be kept clean, otherwise the under surface of 
a wide portion of hide will become soiled with the blacking. 
A wiper or cleaner of some flexible material, held by an 
adjustable bar against the lower surface of the roll, effects the 
cleaning. The material wiped or scraped from the roll drops 
into the trough g and passes to a bucket provided for that 
purpose. 

The rows of bristles on the brush are so arranged that 
alternate rows incline in different directions, those of one row 
inclining toward one end of the cylinder and those of the 
next alternate row toward the opposite end. In this way, 
the ends of the bristles, besides traveling over the leather in 



1 



MANUFACTURE OF LEATHER, PART 3 21 

the direction of rotation of the brush roller, also, when in 
contact with the leather, spring in opposite directions longi- 
tudinally and thus work the blacking backwards and forwards, 
as well as in the direction of the movement of the roller, 
effectually blackening the leather and preventing streaking. 

If the leather is to be dyed, the dyeing may take place imme- 
diately before or after the stuffing, and in some processes 
the dye solution is added in the stuffing drum. 



SHOE, GLOVE, AND FANCY LEATHER 

23. In the "manufacture of the shoe leather, as well as 
glove and fancy leather, there are certain mechanical processes 
which must be followed in order to obtain the desired results. 
As these operations are common to all three of the classes 
mentioned, it will be well to give a description of them here. 

24. Working" Out Skins. — For working out the skins 
in different stages of some processes in light-leather tanning, 
the serial table machine shown in Fig. 9 is largely used. 
Machines of this type are used also for unhairing light skins, 
but they are used mostly for working out and for setting out 
the skins. Through treatment by this type of machine, most 
of the water is removed from the skin, the grain is made fine 
and silky, and the skin is well stretched and left in good 
condition for oiling and drying. 

The rubber-bolstered tables a, a^, and a^ are attached to 
the endless chains h, and are slowly carried between the 
double rolls shown at c and c^. The rolls are spirally bladed, 
and the skins, being carried between the rapidly revolving 
rolls, are subjected to their action both at c and at c^. As the 
machine is constantly in motion, the skin is thrown over 
table a with its backbone lying along the upper edge. The 
table is then carried up and passes between the rolls at c-^. 
When the table is clear of these rolls, the bolsters and skin 
are automatically moved so that the backbone, which was 
not worked between the first pair of rolls, is brought in posi- 
tion to be worked by the second pair of rolls at c. In addition 



22 MANUFACTURE OF LEATHER, PART 3 

to setting out the backbone, the upper rolls perform a second 
working operation on the other parts of the skin. The bolster 




is now moved back to its original position and the table 
descends. The skin is then removed, another skin thrown 
on the table, and the operation repeated indefinitely. 



MANUFACTURE OF LEATHER, PART 3 



23 



The wet skins are put on the tables at one side of the 
machine and the worked skins are removed at the other side, 
so that each operator has the one duty to perform. Recently 
patented inventions provide for the automatic removal of 
the worked skin, so that only one operator is needed for each 
machine. 

25. Sliaving-. — ^After tanning the stock, it is piled on 
horses for a short time to drain free from excess moisture 
and is sometimes pressed and then milled for half an hour 




Fig. 10 

with flour or talc. The skin or sides are then shaved on the 
fiesh to make them smooth and to remove any lumps or 
irregularities in thickness. This work was formerly done by 
hand, but is now almost universally accomplished on the 
shaving machine shown in Fig. 10. The machine" consists of a 
cylinder a, having spiral blades set in its surface. The blades 
are ground by the emery wheel h, which moves from one end 
of the shaving cylinder to the other while constantly revolv- 
ing. The machine being set in motion by a belt shifter, the 



24 



MANUFACTURE OF LEATHER, PART 3 



skin is thrown over the roll c, and pressure on the foot-treadle 
d throws the roll c forwards, bringing the skin in contact with 
the rapidly revolving shaving roll a. The skin is moved by 
the operator so that, by varying the pressure of the skin 
against the shaving roll, any desired amount of shaving may 
be done on any portion of the skin. The spines of the shaving 
roll are constantly being sharpened by the action of the 
grinding wheel h. 

26. Staking-. — After light leathers are dried, it is neces- 
sary to soften and loosen the fibers so that the leather becomes 
soft and pliable. This operation is called staking, and was 
formerly done entirely by hand, the workmen pulling and 




Fig. n 

stretching the skins across a stake, or perch, and using hands 
and knees in the laborious task. In Fig. 11 is shown a repre- 
sentative type of staking machine by which the greater part 
of the staking is done, machine staking having largely super- 
seded the hand method. 

The machine consists of a pair of tongs a and a', the upper 
arm a having at its extremity two felt-covered rolls h and V, 
between which enters the staking blade c, attached to the 
extremity of the lower arm a'. By means of a crank and a 
connecting-rod d the tongs are attached to. the crank-wheel e, 
causing the tongs to move backwards and forwards in the 



MANUFACTURE OF LEATHER, PART 3 25 

divided table /. A cam actuated by the connecting-rod opens 
the jaws of the tongs on the forward stroke, and they are 
closed by springs on the backward stroke. The knee pressure 
regulator g adjusts the pressure of the staking tools on the 
jaws, so that any desired pull on the leather is at the control 
of the operator. 

In staking, one end of the skin is laid against the roll h 
and held by the pressure of the operator's body, the sides of the 
skin being firmly grasped by the hands and inserted between 
the staking jaws of the tongs. The skin is moved about so that 
all parts are subjected to the action of the staking tools, the 
pressure or pull necessary for any particular skin, or for any 
particular part of a skin, being regulated by the lateral move- 
ment of the operator's knee against the pressure regulator g. 

2il, Seasoning-s. — The finishing solutions applied to the 
surface of light leathers are known as seasonings. In addi- 
tion to giving the finished appearance required by the market, 
they serve as a basis for a glaze and make the grain surface 
more elastic. Their composition varies with the class of 
leather being finished, and many materials and combinations 
are used in making the seasoning. For colored leather, a 
mixture of ^gg albumen, flax seed liquor, and gum tragacanth 
is frequently used, and in addition the solution may contain 
some of the dye originally used on the leather. Blood, casein, 
and milk are also used in seasonings for this class of leather. 
Seasonings for black leathers, in addition to the materials 
mentioned, often contain dichromate of soda, logwood liquor, 
isinglass, Irish moss, etc. Skivers and thin skins are often 
treated to seasonings of gums and resins dissolved in alcohol. 

The composition of seasonings is really a matter of experi- 
ence, to be determined by the currier who has watched the 
effects produced by different ingredients and different propor- 
tions of the same ingredients. Each currier has his own for- 
mulas for different effects, and probably no two agree on the 
question of seasonings, except that the seasoning should be 
applied in very light coats and should be well rubbed into the 
leather. 



26 



MANUFACTURE OF LEATHER, PART 3 



28. Surfacing-. — After being properly prepared, the 
leather is submitted to a surfacing process. The surfacing 
operation is sometimes performed by hand, but by far the 
greater part of the leather finished in the United States is 
glazed, rolled, or pebbled by machinery. The operation of 
the surfacing machine shown in Fig. 12 is similar to that of 
the rolling machine used in the manufacture of sole leather, 
but it is lighter in construction. The roller a runs in boxes 
on the end of a beam b connected directly to a wheel c on the 
drive shaft, which imparts a direct backward and forward 
motion to the beam. The end of the beam is supported by a 
pivoted truss d, which also serves as a guide, so that the 




Fig. 12 



MANUFACTURE OF LEATHER, PART 3 27 

roller runs in a line parallel to the face of the bedplate e. 
The bed on which the leather is laid is inclined and its face is 
straight. On all machines for finishing the surface of leather, 
every precaution is taken to guard against oil or grease com- 
ing in contact with the leather. A single grease spot will 
greatly depreciate the market value of a skin. The rolls are 
generally self -oiling and the boxes are especially devised to 
guard against oil leakage. 

29. Glazing-, — For glazing, a smooth roller is used, the 
leather being laid on the bed and moved around under the 
moving roll, so that every part of the surface receives its 
polishing action. The heat essential to a;- good polish, or 
glaze, is supplied by friction of the roll, and the operator 
must be careful not to maintain too great a pressure on the 
leather, or the heat generated will burn the leather. The 
bed is controlled by screws in front of the machine. One 
screw raises or lowers both ends of the bed at the same time, 
another screw regulates the pressure for both ends, and the 
other screws adjust the bed to any desired position. 

For the final finishing, a machine in which a piece of 
smooth, rounded glass is substituted for the roll a, Fig. 12, 
gives the leather a high luster. 

An electrically heated roll that has lately appeared on the 
market has become quite popular. The roller is heated to 
the temperature necessary for a good polish, so that pressure 
need not be resorted to in order to produce heat. 

30. Pebbling". — For pebbling, dicing,^ graining, or for 
giving the leather any desired surface, different rolls are sub- 
stituted for the smooth roll used for rolling and glazing. 
These rolls have their surfaces cut in the desired figure, and 
by the action of the machine the design is imparted to the 
surface of the leather. 

VEGETABLE-TANNED CALFSKINS 

31. Black and colored shoe leathers made from calfskins 
by a vegetable tannage are manufactured in the following 
manner: The skins are soaked, fleshed, and then limed in a 



28 MANUFACTURE OF LEATHER, PART 3 

mixture of lime and red arsenic, or one consisting of lime 
and sodium sulphide. After removing the hair, the skins are 
bated in oropon, or by means of bran or organic acids. After 
washing off the bate, the tanning of the skins begins. Various 
liquors are used in different tanneries, and they are generally 
combinations of two or more tanning agents. Among the 
materials used are hemlock, oak, quebracho, palmetto, and 
gambler. The tanning is done either b)- hanging the skins 
on rockers in the liquors or by the use of a paddle wheel. The 
same general rules for vegetable tanning of heavy leather, 
as to gradual increasing strengths of liquors, are observed, 
but the tanning is conducted with weaker liquors and in such 
a manner as to produce a tough, mellow leather. 

32. After the tanning, the heavier skins may be split and 
the splits retanned in a paddle wheel with either gambler or 
quebracho liquor. The lighter skins are immediately drained, 
pressed, shaved, and they are then ready for stuffing. The 
stuffing is sometimes done with oils, but more often a fat 
liquor made of soap and degras, or soap, oil, and degras, is 
used. After the stuffing, the skins are set out by hand or 
machine, and then dried. The finishing is done by dampen- 
ing the dried skins and then running them in a wheel with 
sumac liquor, so as to prepare them for the coloring. If a 
natural or a lighter color is desired, the skins are sometimes 
cleared by running in the mill first with borax water, follow- 
ing this with an acid solution, and finally washing with pure 
water, after which they are set out by hand or by machine. 
For coloring, the skins are first drummed with a fustic-extract 
solution, and after draining off the extract liquor, the dye 
solution is added to the drum and the drumming continued 
until the coloring is complete. To set the color, the skins 
are then rinsed in a weak solution of alum or other chemical, 
depending on the character of the dye used, and they are then 
set out. When dry, they are slightly dampened in sawdust 
and made soft and pliable by staking on the machine or by 
hand. Then they receive a coat of paste made up of flour 
and tallow, and when this is dry the skins are lightly glazed. 



MANUFACTURE OF LEATHER, PART 3 29 

The seasoning is applied and the skins are glazed and hung 
to dry. After this, another coat of seasoning is appHed, 
followed by a glazing. The stock then receives any desired 
graining, and the leather is ready for market. 

33. If black leather with a purple or yellow flesh side 
is desired, the flesh dye is put in the drum, and the grain dye 
IS applied by machine, on tables by hand, or by folding the 
flesh side together and immersing the folded skin in the dye. 
On vegetable-tanned leather, the black coloring is generally 
effected by a solution of logwood and soda, followed by a 
striker solution made of a soluble iron salt. After the grain 
is dyed, it is washed off with warm water, set out, and a light 
coat of oil given. The leather is then hung up to dry. 

The numerous brands and varieties of vegetable calf leather 
now on the market are produced by varying the finishing 
treatment of tanned calfskins as regards the amount and 
character of stuffing, the character of pastes and seasonings, 
and the luster and style of grain given the leather. The gen- 
eral treatment for all these leathers is as described. How- 
ever, no two factories tan or finish leather by exactly the 
same methods. 

34. Wax Calf. — The class of leather known as wax calf 
has lost its popularity, and hence is not so extensively made 
as formerly. This leather is made from calfskins by a vege- 
table tannage, and is very heavily stuffed with oil, grease, 
and wax. The flesh side is shaved and carefully smoothed 
by hand, and grease black is applied to this side, the grain 
side being left uncolored except for the color of the tanning 
agent used. The finishing is done on the flesh side, and the 
entire skin receives a final oil soaking and is then rubbed to 
give it a final market finish. The grain side being next the 
foot of the wearer of the shoe, the flesh side of the leather is 
exposed to wear, and scratches or scuffs received are easily 
concealed by an application of shoe polish. Because of the 
stuffing used in this class of leather, the clothing is easily soiled 
on coming in contact with the shoe, and this has helped to 
decrease the popularity of this wear-resisting leather. 



30 MANUFACTURE OF LEATHER, PART 3 

During the World War the leather used for army shoes was 
finished on the flesh in somewhat the same manner as described. 
No coloring material, however, was used and so the shoes 
had the natural color of the tanned product. Such leather 
was used only for heavy service, and a leather finished on 
the grain was furnished for shoes intended for ordinary street 
wear. 

VEGETABLE-TANNED SHEEPSKINS 

35. Slieepskins come to the tanner salted, either as they 
are taken from the animal or with the wool removed, the 
skin having been pickled in sulphuric acid and salt solution. 
Large quantities of skins are split and the pickled splits are 
shipped to the tanners in casks. 

Sheepskins are made into a variety of leathers and are 
tanned by processes similar to those used for tanning other 
skins. Considerable sheep leather finds its way into the 
uppers of shoes supposed to have glazed-kid uppers, and 
sheep leather is largely substituted for kid and goat leather 
for other uses. The whole skins are tanned by the oiling 
process, the chrome process, the vegetable process, or by a 
combination of mineral and vegetable tannages, the leather 
being used for shoes, coats, aprons, suspenders, bookbindings, 
linings, etc. When the sheepskins are split, the grain split or 
skiver is generally tanned by vegetable processes for linings, 
sweatbands for hats, bookbindings, gloves, etc. The flesh 
splits, or fleshers, are used for making chamois leather. 

36. Preparation of tlie Skins. — The wool is removed 
from the sheepskin by thoroughly washing the skin first and 
then lightly painting the flesh side with a mixture of lime and 
sulphide of sodium. The skin is then folded along the spine 
line, flesh side in, and piled in low piles to stand until the 
wool slips easily. After the wool is pulled, the skins are 
washed in clean water and put into the limes. After liming, 
the skins are fleshed, washed, and bated, or drenched, in 
organic acids or bran. They are then washed and placed in 
a pickling solution made of salt and sulphuric acid. When the 



MANUFACTURE OF LEATHER, PART 3 31 

pickling is complete, the skins are removed, allowed to drain, 
or are pressed, and are then ready for shipment to the tanner. 
If skivers, or spHts, are to be made, the skins are split by a 
belt-knife machine on coming from the limes. The pickling 
of the skins preserves them and also taws the skins into a 
kind of white leather. 

Sheepskins are very greasy, and, to get the best tanning 
results, the grease must be removed. Sometimes, the skins 
are pressed during the beam-house operations, thus removing 
much of the grease before pickling. Hydraulic presses are 
used and sawdust is sprinkled over the skins to keep them 
from slipping. The. grease is removed by the use of wringers ; 
naphtha is also used to dissolve out the undesirable grease. 

When pickled skins, or splits, are received at the tannery, 
they are first run in a wheel with whiting and salt, borax, or 
borax and whiting, in order to remove any acid. They 
are then washed and given a drenching made of bran and 
salt, after which they are ready for the chosen method of 
tanning. 

37. Tanning- of Sheepskins for Rugs, Fur Coats, 
Etc. — Many sheepskins are tanned without removing the 
v/ool, for rugs, mittens, linings for coats, etc. For such pur- 
poses, the skins are well soaked in water and fleshed. The 
wool is washed thoroughly with a solution of soap and soda 
and rinsed in clean, warm water. The tanning, or tawing, 
is done by means of mixtures of alum, salt, and saltpeter. 
The skins may be allowed to soak in the liquor, or the latter 
is mixed with bran and the paste spread on the flesh side of 
the skin, which is then folded and allowed to remain in con- 
tact with the paste until the tanning is complete. If white 
skins are not desired, the tanning may be done in a liquor made 
of hemlock, gambier, or sumac, which should also contain 
salt and alum. The skins are frequently handled in the tan- 
ning solution, and, when tanned, are washed, drained, oiled, 
dyed, and dried. The alum-tanned skins are frequently 
worked and stretched while drying, so that when dry they 
will be soft and pliable. 



Z2 MANUFACTURE OF LEATHER, PART 3 

38. If the skins are to be white, the wool is scoured with 
a strong soap solution, and the skins are hung in tight rooms 
and subjected to the fumes of burning sulphur to bleach the 
wool. Sodium hypochlorite, permanganate of potash, and 
hydrogen peroxide are also used for bleaching. 

In dyeing the wool on either alum- or bark-tanned skins, 
the wool is first thoroughly washed and rinsed, and the skin 
stretched on a board. The board is lowered into the dye 
bath so that the wool is dyed, and the wool is then rinsed, 
carefully dried, and combed. The wool on bark -tanned skins 
takes a natural dye from the tanning materials used, and this 
is frequently the only dyeing it receives. , 



HOGSKINS 

39. Hogskin leatlier is extensively used for bags, 
saddles, footballs, etc. It is readily tanned by any of the 
vegetable-tanning materials. After the beam-house treatment, 
the skins are tanned in various combinations of oak, hemlock, 
quebracho, or gambler liquors, in paddle wheels, rockers, or 
drums. From 6 to 10 days are required to tan the skins 
thoroughly, and the leather is then cleared, or bleached, by 
running in a solution of borax or soda, followed by an acid 
solution, and finally with clear water. It is then given a 
sumac wheeling, set out by hand, a light coat of oil is given, 
and then it is dried. After drying, the skins are dampened 
and shaved, the heavy skins being split. They are then fat- 
liquored and slowly dried, and allowed to temper for a few 
days. The leather is then dampened and dyed in a wheel, 
set out, oiled, and dried. When ,dry, it is packed in sawdust 
and staked, or gone over with boarding tool, and after receiv- 
ing a light seasoning, it is lightly glazed on the machine, when 
it is ready for shipment. 

TAWING 

40. For making certain classes of white leather, such as 
leather for belt lacings, and glove leather, certain agents that 
are quite different from any previously mentioned, are used. 
Processes requiring the use oi mineral tanning agents were 



MANUFACTURE OF LEATHER, PART 3 33 

originally known as taiving, but the term has been enlarged 
and now includes chrome tanning. 

In tawing, yolks of eggs, flour, alum, and salt are used. 
The hides treated with these agents become tough and pliable, 
can be stuffed, and will not decompose. 

41. Kid-Glove Leatlier. — As an illustration of tawing 
leather, the process for turning lambskins and kidskins into 
glove leather may be described briefly. The skins are thor- 
oughly soaked in cold water for a couple of days and, when 
soft, are put into a revolving drum in which are fixed wooden 
pins that thoroughly shift the skins. Water run through the 
drum while it revolves thoroughly saturates the skins and 
removes the dirt. After washing, they are given a long lim- 
ing in pits, and the excess of lime afterwards removed by 
thorough washing. They are then unhaired and fleshed. After 
further washing in the revolving drum, the skins are bated 
or puered in oropon. After being well washed, they are put 
into the tanning drum with the tanning liquor. This is gen- 
erally composed of a mixture of sulphate of aluminum, sodium 
bicarbonate, salt, flour, egg yolk, and water. 

After running the drum from 12 to 15 hours, the skins 
are taken out and hung up to dry and left in the so-called 
crust or dried condition for several weeks. This treat- 
ment results in a combination of the skin with the aluminum 
sulphate and the leather becomes thoroughly tanned. On 
removal of the skins from the crust, they are brought to a 
sammied condition by dipping in warm water and placing in 
piles. When in the proper soft condition they are knee- 
staked by drawing them over a round blunt knife. This knee- 
staking pulls out the skin to its full dimensions, renders it soft 
and pliable, and at the same time removes any adhering 
material left by the tawing treatment. 

The well-staked skins are buffed to smooth the flesh side, 
given another treatment with egg yolk, and allowed to dry. 
When dry they may be colored or finished in white as desired. 

42. Lace Leatlier. — Another example of tawing is in the 
manufacture of leather for lacing and whips. The hides are 



34 MANUFACTURE OF LEATHER, PART 3 

soaked, depilated in a mixture of lime and sodium sulphide, 
and, after fleshing and unhairing, are washed and bated. They 
are then run in a drum with a mixture of alum, salt, sal soda, 
and bran. After this treatment, they are hung in the loft and 
dried, and when dry, are wet down and a mixture of neatsfoot 
oil, linseed oil, and tallow applied. The hides are then dried 
and, when dry, are slightly dampened and worked by hand or 
on the machine until they are soft and pliable. After the appli- 
cation of another coat of oil, they are ready for the market. 

43. Alum Combination. — Alum-tanned leather, 
although it is tough, has the disadvantage of being thin and, 
when wet, becomes hard. To overcome these drawbacks, it 
is common practice with some grades of leather to retan the 
skins in some form of vegetable tanning material. This retan- 
ning is usually accomplished by running the alum-tanned stock 
in paddles which contain a solution of gambler. By this 
procedure it is not necessary to allow the stock to remain in 
the crust, and the leather may be fat-liquored, colored, and 
finished in a manner similar to that described for straight 
vegetable tannage. 

44. Pyrophospliate Tannage. — A form of alum tan- 
nage which has many points in its favor, consists in adding 
sodium pyrophosphate to the salt and sulphate of aluminum 
mixture. The insoluble aluminum pyrophosphate is readily 
absorbed by the stock and the necessity for crusting is obviated. 
The skin or sides treated by this process may be dried, sam- 
mied, fat-liquored, and finished, or they may be retanned and 
handled like vegetable tanned leather. 

45. Castor and Moclia Leather. — A form of alum- 
tanned leather which is used very largely in glove manufac- 
ture, consists in giving the skins a very long liming, sometimes 
lasting up to two months. By this long-lime treatment the 
grain of the skin is loosened and readily removed by means 
of a blunt knife or stick. The operation of removing the 
grain is known as frizing. The frized skins are then washed, 
bated, and^ drenched, and an alum tannage applied. The 



MANUFACTURE OF LEATHER, PART 3 35 

tanned leather, after staking and buffing, is finished with a 
combination of clay and color. This excessive liming, together 
with the removal of the grain, produces the soft, pliable 
appearance of this class of leather. 



OIL TANNAGE 

46. Cliainois Leatlier. — The so-called chamois leather 
is made from the fleshers, or flesh splits, of sheepskins. The 
splits are thoroughly washed and may be bran-drenched, after 
which they are pressed to remove the excess of water. They 
are then thrown into a heavy machine similar to the hide mill 
used in sole-leather tanneries and worked with cod oil or a 
good grade of fish oil. Several additions of oil are made 
while the skins are being worked in the beaters, and the 
operation of beating consumes much time. When the opera- 
tion is ended, the skins are removed from the mills, or beaters, 
and arranged in piles or hung in closed rooms. This causes 
the skins to heat, completing the oxidation of the oil that has 
been beaten into the skins. After this treatment, the skins are 
placed in a hydraulic press and the excess of oil and grease 
pressed out. The product of this pressing is known as degras 
and is used in the finishing of many kinds of leather. After 
this pressing, the skins are washed in a solution of sal soda, 
which saponifies any remaining oil and grease. The soap thus 
formed is treated with weak sulphuric acid, which releases 
the fatty acids. This oil is the sod oil of the currier. After 
the removal of the oil, the skins are washed, dried, staked, 
and made smooth and pliable by working, when they are 
ready for market. 

47. Oil-Tanned Slieepskins. — Another example of an 
oil-tannage production is the old Napa leather, which is really 
a soap-and-oil-tannage product and not the result of a pure 
oil tannage, as is chamois leather. The wool is removed from 
the skins by painting on the flesh side with a mixture of lime 
and sulphide of sodium, and the skins are thoroughly washed 

393—9 



36 MANUFACTURE OF LEATHER, PART 3 

and then pressed in a hydraulic press to remove the grease. 
The skins are then run into a revolving drum containing a 
solution of salt and sal soda, or potash. From this solution, they 
are removed and pressed, or wrung, and run into a drum 
with a solution containing soap and neatsfoot oil. When this 
solution has penetrated the skins, they are removed and 
pressed. The heavier skins are returned to be retanned, while 
the lighter skins are colored and dried. When dry, they are 
moistened and staked and then stretched and tacked on frames 
and thoroughly dried. When dry, they are buffed, or shaved, 
and finished to the desired dull or glazed finish. 

This leather is soft and possesses considerable strength, 
being largely used for linings, bookbindings, and as trimming 
for fancy braces and suspenders. 

48. Buckskins. — In the manufacture of buckskin leather, 
deer skins are the raw material used. The skins are given a 
long lime treatment, usually extending over forty days. The 
grain, having become loosened, is removed by frizing and after 
bating and drenching, they are given an oil tannage similar 
to that described under Chamois Leather. The finished stock 
is usually hung out in the air to bleach. 

In place of cod-liver oil, it has been found that other oils 
may be used. The author has been especially successful in 
substituting the oil from shark liver for cod-liver oil. 

49. Lace Leatliers. — Lace leather must be especially 
strong, as it is used for joining machinery belting. A good 
lace leather may be obtained by milling side leathers out of 
the bate in a mixture of cod oil arid tallow. The milled stock 
is well set out and allowed to dry very slowly. 

50. A process devised by the author and one which is 
giving very satisfactory results, consists in the use of a com- 
bination of alum and oil tannage. The process is carried out 
by using a short liming process followed by bating with oropon 
and then pickling with salt and sulphuric acid. The pickled 
stock is then milled in a 5° Be. salt solution, to which has been 



MANUFACTURE OF LEATHER, PART 3 Zl 

added 7 per cent, of suphate of aluminum and 2 per cent, of 
borax. The stock, after being milled for 3 hours, is allowed 
to rest in the exhaust liquor overnight, after which it is set 
out, and hung up to dry. When bone-dry, the sides are sam- 
mied back to a 30 per cent, moisture content and milled with 
shark-liver oil. The amount of oil required is one-half gallon 
per side. One-fourth of the oil required is added to the 
stock in the mill and turned for one hour. A second quarter 
is then added and milled for another hour, and then the third 
quarter is added and milled for two hours. The stock is then 
removed from the drum and piled down overnight. The fol- 
lowing day the stock is returned to the drum and the remainder 
of the oil added. The stock is then run for two hours, and 
with a lattice door run for another hour. From the drum 
the stock is well set out, rubbed with shark-liver oil and 
tallow, and hung up to dry. When thoroughly dry, the sides 
are sammied lightly and allowed to remain in piles overnight, 
care being taken that they do not overheat. They are then 
set out again, rolled, and hung up to dry. 

51. Combination Tanned Buckskins. — On the weight 
of the pickled stock, triturate 5 per cent, of flour with a small 
amount of water. Dissolve 3 per cent, of sulphate of aluminum 
and 2 per cent, of salt in 20 per cent, of water. Slowly add 
to this solution 0.25 per cent, of sodium bicarbonate; mix in 
1.5 per cent, of ^%g yolk and 0.1 per cent, of olive oil. Now 
add the flour paste. The skins being placed in the drum, the 
above mixture is introduced, the stock run for two hours, 
then left in the liquor overnight. The following morning the 
mill is run for one-half hour, the excess of liquor drawn, and 
a solution of 10 per cent, of gambier at 19° Bk. with 10 per 
cent, of salt introduced. The mill is run for \\ hours. The 
stock is now fat-liquored with 3 per cent, of acid-fat liquor 
and hung up to dry. When perfectly dry, the stock is sam- 
mied, staked, buffed, and retanned with 5 per cent, of gambier, 
washed, set out, oiled oflf with glycerine, and tacked. After 
stuffing the stock is given a light season of flaxseed liquor and 
milk, rolled while damp, staked, dried, restaked, and blacked. 



38 MANUFACTURE OF LEATHER, PART 3 



CHROME TANNING 

52. A typical example of mineral tannage is the chrome 
process. This tannage is purely a chemical one, consisting o£ 
the combination of chromic oxide with the skin. This com- 
bination is evidently a chemical one between the skin and the 
oxide, as the product is not affected by washing or boiling, 
as are the products of bark tannages ; neither is there any 
deposition of the oxide after the chemical union has taken 
place, even in the basic liquors used in one of the processes. 
Chrome leather is tanned either by the tzvo-bath process or the 
one-hath method, 

53. Two-Batli Cliroine-Tanning- Process. — The 

Schultz process of chrome tanning consists in treating the skins 
to a bath of dichromate of soda in the presence of a mineral 
acid. Following this, a bath of a solution of soda is given. The 
theory of this process is based on the formation of chromium 
oxide, having the formula Cr^O^, which is deposited on and 
combines with the skins. A solution of dichromate of soda 
and hydrochloric acid is made up in the proportion of about 5 
pounds of dichromate and 2.5 pounds of hydrochloric acid, 
specific gravity 1.16, to every 100 pounds of wet prepared 
skins. 

The reaction expected between the acid and the dichromate 
is 

Na^Cr^O,+2HCl = 2NaCl+H^O+2CrO^ 

However, in the process, only two-thirds of the acid neces- 
sary for the complete reaction, is' used, and it is not safe 
to say, considering the peculiar properties of chromium, that 
this equation exactly represents the reaction which takes place. 

After the skins have been struck through in this bath, they 
are put into a solution of thiosulphate of soda and hydro- 
chloric acid, which effects the reduction of the CrO^ to Cr^O^. 
To neutralize the acid remaining in the skins, they are after- 
wards wheeled with water containing suspended calcium car- 
bonate, or a solution of borax or sodium bicarbonate. 



MANUFACTURE OF LEATHER, PART 3 39 

54. The use of practically all the agents that will reduce 
CrO^y as hydrogen sulphide, the sulphides, bisulphites, etc., has 
been patented. Sulphurous acid seems to be the best, or, at 
least, it is one of the most generally used. Norris has patented 
the use of zinc in the hypo bath, which, it is claimed, accom- 
plishes a more rapid and economical reduction. 

By using sodium dichromate and sulphuric acid, it is possible 
to effect the reduction with sodium bisulphite and thus elim- 
inate the production of free sulphur as is the case where 
sodium thiosulphate and acid are employed in the reducing 
bath. 

Amend has a two-bath process in which chromic acid, HrX^rO^^^ 
replaces the dichromate and an acid of the Schultz patent. This 
requires careful manipulation. He suggests the use of aniline 
as a reducing agent. 

A chalk bath after the tanning bath neutralizes the hydro- 
chloric and sulphurous acids remaining in the skins. Solu- 
tions of sal soda, sodium bicarbonate, and borax are also used 
for the same purpose. Norris has patented the use of potas- 
sium permanganate for this purpose. This salt not only 
oxidizes the sulphurous acid to sulphuric acid and neutralizes 
it at the same time, but it also precipitates the oxide of man- 
ganese on the skin, and this acts as a mordant in subsequent 
dyeing. 

55. One-Bath. dirome-Tanning- Process. — The one- 
bath chrome process of chrome-tanning, brought to perfection 
by Martin Dennis, and now used by many manufacturers, 
offers less difficulty than the two-bath system and has largely 
replaced it for all grades and classes of stocks excepting goat- 
skins. 

In this process only one bath is used ; this is composed of 
a solution of a basic chrome salt that readily yields its excess 
of chromic oxide to the hide tissues. The tanning liquor, as 
originally prepared, was made by dissolving oxide of chromium 
in hydrochloric acid, thus forming the normal chloride. To 
this was added an alkaline base, as sal soda, this stronger base 
taking from the chromium chloride part of its acid, leaving 



40 MANUFACTURE OF LEATHER, PART 3 



the oxy, or basic salt. This basic salt is a very unstable 
compound and readily yields its excess of chromium to any- 
thing having an affinity for it, which, in this case, is the hide 
substance. The advantages of this system over the two-bath 
system are as follows : 

1. One handling of the skins is saved, because one bath 
only is needed for the tanning. 

2. The skins are not exposed to the destructive action of 
chromic acid, and are therefore stronger, with more lasting 
suppleness, and have a better grain. 

3. There are no offensive fumes evolved in this process ; 
the reduction of the oxide in the two-bath process is accom- 
panied by a strong odor of sulphur dioxide. 

4. The skins are not harmed by too long contact with the 
tanning liquor. 

5. Less skill is required to operate it and the bath itself 
is cheaper. 

56. The practical operations of tanning by means of the 
one-bath system are as follows : 

The skins or hides are soaked, limed, unhaired, fleshed, and 
bated as usual. From the bate they are taken to a drum and 
pickled with a solution of salt and sulphuric acid in the pro- 
portion of 12 per cent, salt with IJ per cent, of sulphuric acid 
at a density of 12° Be. This keeps the skins open and plump 
and also has the effect of keeping them in good condition 
during and after tanning. From the pickle they are put in 
the tanning bath, which contains a solution of the concentrated 
basic chrome liquor, 3 per cent, of Cr^O^ on the weight of the 
stock, and also 10 per cent, of common salt. This common 
salt prevents the grain of the leather from drawing imder the 
astringent action of the chrome bath. 

When the skins have assumed a uniform greenish-blue color 
and a cutting reveals the completion of the process, they are 
neutralized with 1 per cent, of sodium bicarbonate and horsed 
up overnight. The next day they are rinsed in clean water 
and worked on the flesh side with a slicker on a perfectly 



1 



MANUFACTURE OF LEATHER, PART 3 41 

clean table or they are set out on the machine. They are next 
shaved and sorted for colors and blacks. 

57. Since Martin Dennis made practical use of one-bath 
chrome liquor, many other concerns have entered the field. 
As a result of investigation, many methods for preparing one- 
bath chrome liquors have been developed. The simplest 
method of preparing this liquor, and the one used by many 
tanners, consists in reducing sodium dichromate in the pres- 
ence of an acid. A formula which gives very satisfactory 
results is as follows : 

Dissolve 20 pounds of sodium dichromate in 25 gallons of 
water. To this add 10 pounds of sulphuric acid and 20 pounds 
of salt. In a separate container dissolve 22 pounds of sodium 
bisulphite in 10 gallons of water, and add this solution very 
slowly and with constant stirring to the solution of chrome. 
The resulting liquor should be blue-green in color; if not, 
a little more sodium bisulphite should be added. When com- 
pletely reduced, add enough water to make 40 gallons and 
use this as a stock solution. To tan with this liquor, use 8 
gallons for each 100 pounds of the pickled stock. 

58. Cliaracteristics of Cliroiiie Leatlier, — Chrome 
leather has special and peculiar qualities that distinguish it 
from other kinds of leather and which make it a superior 
article. It is not actually waterproof, but rather a moisture 
resister. It is a difficult matter to wet it thoroughly when 
once perfectly dry. 

The ordinary bark tannages are compounds of two organic 
materials and when they are subjected to alternate wetting 
and drying, they will eventually deteriorate and become rotten. 
Chrome leather, being a combination of an inorganic material 
with the hide substance, is not affected by wetting and dry- 
ing. It is lighter than bark leather and also possesses more 
elasticity and > is of greater strength. 

59. Cliroine Combination. — For certain uses straight 
chrome leather does not answer all of the requirements. Tan- 
ners have, therefore, found it desirable to after-treat or retan 



42 MANUFACTURE OF LEATHER, PART 3 



1 



the chrome stock. This is done by running the skins in a 
solution of some vegetable tanning material. The so-called 
washable cape leather used extensively in glove manufacture 
is produced by first tanning the skins in chrome and sub- 
sequently retanning in gambler extract. The skins are then 
well fat-liquored, dried, sammied, staked, buffed and colored. 

60. Fat-Liquoring. — The finishing, or currying, of 
chrome leather is carried out with some modifications of the 
methods used for finishing bark leather. Chrome leather must 
be stuffed soon after removal from the tanning bath and must 
not be allowed to become dry. The most efficient way of 
stuffing chrome-leather is by fat liquoring. There are differ- 
ent ways of making and using these fat liquors, depending on 
the quality of the leather to be produced. 

The fat liquor most commonly used consists of some form 
of sulphonated oil which produces an emulsion with water 
and which is readily taken up by the stock. Soap mixed with 
neatsfoot oil is very largely used in the fat-liquoring of goat- 
skins for glazed kid. Either sulphonated oil or soap may be 
employed to carry in other materials such as egg yolk, degras, 
cod-liver oil, and the like. The amount and nature of the 
oil used regulates the character of the finished product; the 
more oil employed, the softer will be the resulting leather. 

61. There are on the market many varieties of chrome 
leather that are sold under different trade-names. When these 
varieties of leather represent the product of straight chrome 
tannages, the actual tannage of each particular brand is car- 
ried out in the same way, the differences that characterize 
them being due to the amount and character of stuffing, char- 
acter of the finish, and the style of grain given the finished 
leather. 

62. Box Calf. — The variety of leather known as box 
calf is generally made in the following manner: The skins 
are soaked, limed in a mixture of Hme and red arsenic, or of 
lime and sodium sulphide, fleshed, unhaired, and bated. They 
are then pickled in a solution of sulphuric acid and salt and 



MANUFACTURE OF LEATHER, PART 3 43 

tanned by either the one-bath or the two-bath chrome process. 
The skins are then pressed in a hydrauHc press, or worked out 
by hand or machine, and shaved to give the flesh side a 
smooth surface. They are then stuffed, or fat-hquored, and 
colored. After hand or machine setting out, to remove the 
excess water, they are dried simply by hanging them over 
poles in the loft. When the leather is dry, it is packed in 
damp sawdust, and when properly sammied, it is staked by 
machinery. The well-staked skins are then tacked out on 
frames and allowed to dry under tension. When thoroughly 
dry the skins are stripped from the boards and given a coat 
of season. This season may be made up in several ways but 
usually contains some gelatinous or albuminous material to 
which coloring matter has been added. The commonest color 
is black and is produced by adding a solution of logwood and 
iron to the compound. The skins after seasoning are hung 
up to dry. When the season has become set and the skins 
are thoroughly dry, they are glazed on the machine and a 
second coat of season applied. The skins are again glazed, 
which operation may be repeated several times before board- 
ing. The box grain of the leather is given by a workman, 
who has a cork-covered boarding tool strapped to his fore- 
arm. The boarding tool is applied to a fold of the leather, 
and the characteristic grain imparted to the leather by the 
motion and pressure exerted by the workman. 

63. Briglit Finish. Calf. — In producing a bright finish 
on chrome calf, the same operations are carried out as for 
box calf, except that a shorter liming is applied and the final 
glaze finish contains either blood or Ggg albumen. The opera- 
tion of boarding is, of course, omitted. 

64. Matt Calf. — When, a dull finish is required, the 
same operation is carried out as for bright finish except that the 
season employed does not contain any albuminous material. 
The dull effect is produced on a smooth plate machine or by the 
application of a hot flatiron. After ironing, the stock is oiled 
off with a light mineral oil which gives the final pleasing 
appearance to the leather. 

393—10 



44 MANUFACTURE OF LEATHER, PART 3 

65. Glazed Kid. — Goat skins, usually imported in a 
dried state, are used in making both glazed, white and dull 
kid, although some sheep leather and :ven some light grain 
splits are sold to be used in glased-kid shoes. The dried goat 
skins are well soaked and then painted on the flesh side with 
a mixture of sodium sulphide and lime. This attacks the 
roots of the hair, loosening it, and causing it to slip easily. 
After painting, the skins are folded along the spine, flesh 
side in, and piled in low piles to lie overnight. In the morn- 
ing the hair is removed and the skins limed. In the lime 
liquor a mixture of lime and red arsenic is used. The skins 
after beaming are washed in paddle wheels to remove some 
of the lime and sodium sulphide used for unhairing. After 
fleshing, the skins are bated, or puered, with dog-manure or 
oropon to the proper condition for tanning. Either the one- 
or the two-bath chrome process is used for tanning, the latter 
being the more popular. After being run in the first bath in 
a drum, the skins are removed and set out on a machine, or 
pressed in a hydraulic press, to remove the excess of liquor. 
They are then dipped by hand in a solution of hydrochloric 
acid and hyposulphite of soda and placed in covered piles. 
This hand-dipping is for the purpose of reducing some of 
the chromium solution on the surface of the skins. The next 
day the skins are taken from the piles and run in a drum with 
the second bath, which reduces and fixes the chromium oxide 
on the fibers. Some tanners prefer to neutralize in a paddle 
rather than in the drum. 

66. When the reduction is complete, the skins are run 
with sodium or bicarbonate solution until the free acid has 
been neutralized, and finally they are w^ashed with clean water. 
The skins are then set out by hand or by machine to remove 
the excess of water, fat-liquored, and given the desired color, 
after which they are worked by hand or machine to remove 
moisture and to give them a soft silky grain and also to 
stretch them. The skins then receive a light coat of glycerine, 
or of glycerine and oil, on the flesh side and are dried on 
poles in a warm drying-loft. When thoroughly dry, they 



MANUFACTURE OF LEATHER, PART 3 45 

are taken to an airy loft, thrown in piles, and left to temper 
for 7 or 8 days, during which time they absorb atmospheric 
moisture, and soften. After tempering, the skins are packed 
in damp sawdust, which brings them to a proper condition 
for staking. The staking is done either by hand or by 
machine, the smaller and lighter skins being generally hand- 
and-knee-staked, while the machine is used on the larger and 
heavier skins. After being thoroughly broken and softened 
by the staking, a coat of heavy seasoning is applied, and after 
this is dry the skins are lightly glazed on a glazing machine. 
Seasonings vary in composition with the finisher, but they 
are generally compounds of such materials as blood albumen, 
egg albumen, algin, etc., and are colored to match the color 
of the leather that is being finished. After the first seasoning 
and glazing, a second coat of lighter seasoning is applied, and 
the leather receives a heavier glazing on the machine. A final 
light coat of seasoning is applied, and the skins are then 
glazed with a heavy pressure, after which they are laid away 
to be inspected, sorted, measured, and packed for shipment. 

67. For dull-finished leather, a heavier stuffing, or fat- 
liquoring, is given the most perfect of the skins and, instead of 
being glazed by the machine, they receive a light coat of paraf- 
fin oil and are ironed by hand with a hot flatiron. They may 
then receive another coat of oil and receive a final ironing. 

68. Chrome side leather is made by soaking, liming, unhair- 
ing, fleshing, and bating the whole cowhide, and then pickling 
it in salt and sulphuric acid, and spHtting. The grain split is 
then chrome-tanned and the subsequent finishing processes 
are the same as for either glazed or dull kid. Heavier grain 
splits may be tanned and finished in a manner similar to that 
employed with chrome calf, and frequently the entire cowhide 
is chrome-tanned before splitting. 

69. Clironie Patent Leather. — Whole skins, such as 
calf, goat, and kid, or split cowhides and steer hides are used 
in making enameled, or patent, leather for shoes. The actual 
tanning processes for leather to be coated are similar to the 



46 MANUFACTURE OF LEATHER, PART 3 

methods of tanning different skins or hides into other Hght 
leathers. The fat-Hquoring and seasoning vary somewhat, 
but up to the point of enameling, the process is not materially 
different. 

70. A patent shoe leather made from chrome-tanned cow- 
hide splits is made by the following process : The hides are 
soaked, split into sides, fleshed, depilated with lime and sodium 
sulphide, washed, and bated. They are then pickled in a 
solution of sulphuric acid and salt, and are either pressed or 
put through a wringer and then sent to the splitting machine. 
The grain split is used for making the patent leather, and 
after being shaved on the machine to give it uniform thick- 
ness and to make the flesh side smooth, it is tanned by a one- 
bath chrome process. It is then fat-liquored and colored, the 
flesh receiving a purple color before the main dyeing takes 
place. After setting out by hand or on the machine, the grain 
side receives a light oiling, and the split is then sent to the 
loft and dried. When dry, it is packed in wet sawdust, then 
staked by the machine and carefully tacked. The leather on 
being stripped is usually degreased and is then ready to receive 
the enameling compounds. These are made in various ways, the 
pastes used on the first coats being generally made by boiling 
down linseed oil with lampblack and adding naphtha to thin 
them. Other oils and mixtures are used for this purpose, their 
ingredients differing with each foreman, who endeavors to keep 
his competitors from securing his formulas. The leather is 
stretched and tied to frames, after which the first coat of daub is 
rubbed on and worked over the surface evenly, all surplus 
being removed by means of a slicker. When the first coat 
has dried, a second coat of the same material is applied in the 
same manner, and the frame, with the leather, is placed hori- 
zontally in a large oven to dry. If other coats are to be 
applied before the top varnish, they are put on after this 
drying and the frame returned to the oven. When the leather 
is ready for the top varnish, it is gone over with pumice to 
make the surface perfectly smooth and to remove pimples. 
The dust from this operation is brushed off the leather, or 



MANUFACTURE OF LEATHER, PART 3 47 

blown off by a jet of compressed air. The top varnish is 
applied in a warm, dust-proof room, into which the ovens 
open. It is thinner than the previous coating solutions and 
varies in composition. Linseed oil, organic gums, pyroxylin, 
or guncotton, camphor, amyl acetate, wood alcohol, and castor 
oil are among the ingredients of the various daubs and var- 
nishes used for coating leather, and probably no two factories 
use the same formula. The top varnish is applied to the 
leather with a broad, long-bristled brush similar to a white- 
wash brush. In applying this top coat, great care is taken to 
spread it evenly and to leave no bubbles or dust or hair marks. 
After receiving the top varnish, the frame is placed in the 
oven and the skin dried, and after the oven drying it is taken 
into the air to i eceive a final sun-and-air drying, which removes 
any tendency to stickiness. When thoroughly dried, the fin- 
ished leather is cut from the frame, trimmed, and measured, 
when it is ready for shipment. 

71. Chrome sole and belting leathers are being made in 
constantly increasing quantity, although as yet this class of 
tannage has not become common. The sole and belting leather 
produced by the chrome-tanning process has not the weight 
of the bark-tanned leather it aims to supersede, and its cost is 
accordingly higher. The cowhides or steer hides from which 
these kinds of leather are made, go through the regular beam- 
house processes, being bated so that all the lime is removed 
from the hides. Then they are pickled in a solution of sul- 
phuric acid and salt, and when drained after removal from 
this solution they are ready for the tanning. The one-bath 
chrome process has been found most suitable for this class 
of leather. The pickled hides are usually tanned on the 
paddles, as the constant tumbling of such heavy stock in a 
drum is apt to produce a loose grain. The liquor is first made 
up by preparing a 10° Be. salt solution and then adding an 
excess of the one-bath chrome liquor. The time of the treat- 
ment varies from 12 to 48 hours, depending upon the nature 
of the tan liquor. A few tanners carry on the operation in 
rocker pits, but such practice is not very common. 



48 MANUFACTURE OF LEATHER, PART 3 

After being tanned so as to stand the boil, the hides are 
removed from the paddle and horsed up overnight. They 
are then shaved, neutralized, washed, and fat-liquored. For 
sole leather the fat-liquoring is only slight and some tanners 
do not give the hides any oil. Where the stock is fat-liquored, 
it is tacked while still wet and allowed to dry under tension. 
This drying under tension results in a stiff leather which is 
desirable for this kind of stock. If the leather is to be made 
waterproof, it is dipped into hot wax and immediately trans- 
ferred to the hot room to drain. Some shoe manufacturers 
prefer to purchase the chrome sole and do their own water- 
proofing. 

When heavy chrome leather is to be used for belting pur- 
poses, it is fat-liquored somewhat higher than sole leather 
but is afterwards dipped to make it stronger and more water- 
proof. In place of tacking, leather to be used for belting is 
usually cut in strips and dried under tension in stretching 
frames. 

72. Chrome Combination. — Straight chrome sole 
leather is more difficult to work then vegetable-tanned stock 
and does not channel or buff very satisfactorily. This objec- 
tion may be overcome by retanning the hide with a vegetable 
tanning agent. A ten-day treatment with 40° Be. extract will 
fill the stock, add weight, and improve its appearance. Stock 
which has been retanned in this way may also be loaded in 
the extract wheel and made to carry considerable weight. 
Chrome retanned leather is usually waterproofed in the same 
manner as straight chrome. Chrome retanned sole leather 
may be worked like vegetable-tanned stock and can be chan- 
neled and burnished with ease. 



DONGOLA LEATHER 

73. An example of a combination vegetable and mineral 
tannage is found in the so-called dongola leather. Originally, 
the dongola tannage was a combination of alum and gambier, 
but dongola leather is now made with vegetable combinations 
other than gambier. Hemlock and oak liquors are sometimes 



MANUFACTURE OF LEATHER, PART 3 49 

used in combination with gambier, and quebracho extract is 
also a popular material for use with gambier. This class of 
tannage is applied to calfskins, sheepskins, goatskins, kidskins, 
and side leathers. 

74. Preparation of Dongola Leather. — After coming 
from the beam house, the skins are bated and washed and 
then pickled in a solution of sulphuric acid and salt. After 
pickling, the skins go into the tan liquor, which is made up 
of gambier, gambier and quebracho, gambier and hemlock, 
etc., to which is added a solution of alum and salt. The 
tanning takes place in rockers or in paddle-wheel vats. In 
some tanneries, the stock is given the mineral and then the 
vegetable tanning, the skins being first tawed in the alum 
and salt liquor and then tanned in the vegetable tan liquor. 

After tanning, the leather is washed in a wheel, pressed or 
wrung, and then shaved ; if splitting is necessary, it is done 
at this stage. Sometimes, the heavy hides are split out of 
the pickle, the flesh splits being tanned by a dongola process, 
while the grains are finished by a chrome process. 

After shaving or splitting, the leather generally receives a 
wheel treatment with a pure gambier or sumac liquor. Splits 
are retanned in gambier or quebracho liquor in a wheel, or 
they may be returned to the original tanning vats. 

From the sumac wheel, the leather is piled on horses and 
allowed to drain overnight ; or, it may be set out immediately 
and then stuffed. The stuffing is done by a fat liquor gener- 
ally made of soap, cod oil, and degras. Frequently, the 
leather is given two stuffings, the first being a straight-oil 
combination, such as neatsfoot and cod oils. Then, after 
drying and redampening, the leather is again stuffed with a 
fat liquor. After stuffing, the leather is dried. When dry, 
it is dampened in a wheel with warm water and is then 
colored and finished according to the character and appear- 
ance desired in the finished product. 



50 MANUFACTURE OF LEATHER, PART 3 



LEATHER DYEING 

75. Dyeing- and Finisliing of Leather. — ^Dyes are 
applied to leather by brushing by hand or on the machine, by 
means of the paddle, or mill, or on the tray. In the brushing 
method a solution is spread evenly over the grain on the flesh 
side by means of a stiff brush and then hung up to dry. In 
tray dyeing the skins are either folded down the back or two 
skins are placed flesh to flesh and then drawn several times 
through the color solution. When a large number of skins 
or sides are to be dyed the same color, the paddle or mill is 
employed. In paddle coloring, the necessary quantity of dye- 
stuff is dissolved in the water and while the paddle is turning 
the stock is carefully introduced. By far the largest amount 
of leather is colored in the mill, in which case the skins are 
placed in the drum and enough water introduced to cover the 
stock. The mill is then set in motion and the color solution 
slowly added through the trunnion. 

In coloring leather both natural dyewood extract and coal- 
tar colors are applied. Of the natural dyes, logwood, fustic, 
and osage orange are most commonly used. Of the coal-tar 
colors, basic acid, direct and alizarine dyes are employed. 

As the methods used for coloring chrome-tanned leather may 
be applied equally well to vegetable-tanned stock, we will 
illustrate the various procedures on this kind of leather. 

76. Black. — The shaved stock, after being weighed, is 
placed in the mill and enough water at 125° F. added to float 
the skins. One per cent, hematin on the weight of the stock 
is dissolved in water at 125° F. and, being made alkaline with 
ammonia, is introduced through the trunnion while the drum 
is in motion and turned for fifteen minutes. One and a half 
per cent, of direct leather black is dissolved in water at 145° 
F. and added through the trunnion to the contents of the 
drum and run for 15 minutes longer. Without removing the 
excess of color, a sulphonated oil fat-liquor is introduced into 
the mill turned for another half hour. The stock is then 
washed, oiled off with Setine No. 2 and hung up to dry. 



MANUFACTURE OF LEATHER, PART 3 nl 

77. Dark Tan. — The shaved stock is placed in the mill 
and sufficient water added at 125° to float the stock. While 
the mill is in motion a solution 3 per cent, of fustic is 
introduced through the trunnion and the milling continued 
for one-half hour. A solution of one-fourth of one per cent, 
of potassium titanium oxalate is now added and run for 15 
minutes. The stock is then washed for 5 minutes with warm 
running water, enough being allowed to remain to float the 
stock, and the following dye solution introduced. For each 
100 pounds of skins make up 

Flavo phosphine G. G. Cone, 22 oz. ; vesuvine R., 3 oz. ; 
methylene blue B., J oz. ; water at 140° F., 10 gals. 

While the mill is in motion one-third of the color is intro- 
duced through the trunnion. At the expiration of 5 minutes 
a second third is added, and after another 5 minutes the final 
portion is introduced. The mill is then run for one-half 
hour, the stock washed in running water and fat-liquored 
with a good grade of sulphonated oil. The skins should then 
be set out carefully and hung up to dry. 

78. Dyeing: with Acid or Direct Colors. — The shaved 
skins are placed in the drum and sufficient water added at 
125° F. to float the stock. The color solution is prepared by 
dissolving the necessary quantity of dyestufif in water to which 
is added about 1 per cent, of borax. The color solution is 
introduced in 3 portions and the stock milled for one-half 
hour. By this time the color has penetrated the leather and 
is set by adding 3 per cent, of formic acid diluted with water 
and run for 15 minutes. The excess of color is drawn off 
and the stock fat-liquored with sulphonated oil. The skins 
are then set out and hung up to dry. 

79. Sammie. — The skins as they come back from the 
dry- room are stiflf and so must be softened back. This is done 
either by dipping in warm water and placing in piles to sammie 
or they are packed down in damp sawdust for several hours. 

80. Staking-. — In order to stretch the skins they are 
worked in a staking machine. 



52 



MANUFACTURE OF LEATHER, PART 3 



81. Tacking, — After staking the skins are sent to the 
tacking loft and while still damp are carefully tacked on frames 
and allowed again to dry. 

82. Finisliing. — On stripping from the frames the skins 
are given a coat of season and while slightly damp, are rolled 
on the jack. They may then be finished in matt or bright as 
desired by using the proper solution and either ironing or 
glazing. 

MEASUREMENT OF LEATHER 

83. Sole leather is always sold by weight, but light leathers 
are sold by area, the approximate thickness also being taken 
into consideration. The measurement of leather is now 




Fig. 13 



MANUFACTURE OF LEATHER, PART 3 



53 



usually done by means of machines, of which there are several 
on the market. Some of these vary essentially in principle, but 
the descriptions of the Sawyer and Union measuring machines 
given here will be sufficient to show their application. 

84. Sawyer Measuring Macliine. — The Sawyer 
leather-measuring machine, shown in Fig. 13, is run by 
power. The leather is fed between two rollers that smooth 
it out and bring it into contact with small measuring wheels. 
The movement of these wheels influences properly arranged 
levers, which, in turn, affect the index of the registering 
mechanism. 

85. Union Measuring" Macliine. — The Union leather- 
measuring machine, shown in Fig. 14, consists of a table with 
a top made of parallel sticks of wood. A hinged cover closes 




Fig. 14 



54 MANUFACTURE OF LEATHER, PART 3 



over this, and throughout the entire surface of this cover 
are suspended small wire pins that are free to slide up 
through holes in the cover. The pins are arranged in 
rows, so that when the cover is down, with nothing between, 
the pins hang between the strips of wood forming the lower 
table. 

When leather is to be measured, it is placed on these strips 
and the top brought down over it. The surface of the leather 
obstructs the small pins and throws them up, the ends of the 
remaining pins dropping between the strips. These pins are 
of such sizes and weights that each exercises the same force 
on a spring balance above, so that this device is affected by 
the number of pins obstructed by the leather. The weight of 
forty-eight of the pins corresponds to a square foot of area, 
and the dial of the balance indicates, in fractions of a square 
foot, the weight released by the leather, and consequently 
the area of the leather. 



I 



